An invisible creature is impossible to see without the aid of magic or a special sense. For the purpose of hiding, the creature is heavily obscured. The creature's location can be detected by any noise it makes or any tracks it leaves.
Attack rolls against the creature have disadvantage, and the creature's attack rolls have advantage.
So you need magic or special senses, or the invisible creature needs to make noise or leave tracks. (I would imagine an invisible flying Sprite leaves no tracks and makes very little noise.) The one thing I find very interesting here is that for the purpose of hiding the creature is considered heavily obscured.
A heavily obscured area—such as darkness, opaque fog, or dense foliage—blocks vision entirely. A creature effectively suffers from the blinded condition when trying to see something in that area.
So, 1. If something is invisible treat it as trying to see in heavy obscured conditions. And, 2. A creature suffers the blinded condition trying to see something in that area.
Blinded
A blinded creature can't see and automatically fails any ability check that requires sight.
Attack rolls against the creature have advantage, and the creature's attack rolls have disadvantage.
So, Invisible = Heavily Obscured. And Heavily Obscured = Blinded. And Blinded = auto fails any ability checks that require sight... like the Perception check (passive or not) made to detect an hidden invisible creature. (like a Sprite with +8 to Stealth)
I mean having disadvantage to find such a creature is one thing but to have anyone auto fail when trying to find the hidden invisible Sprite is really cool.)
"A rightful place awaits you in the Realms Above, in the Land of the Great Light. Come in peace, and live beneath the sun again, where trees and flowers grow."
— The message of Eilistraee to all decent drow.
"Run thy sword across my chains, Silver Lady, that I may join your dance.”
What you're glossing over is that you automatically fail an ability check that "requires sight," and only in relation to that Invisible creature itself.
That "requires (sense)" terminology is something that 5E uses in a lot of different places. See various monsters with Keen Senses like a Wolf, or an Owl, or things like Sunlight Sensitivity on a Drow. To some extent, Perception always uses all of your senses, but a specific Perception check might be asked for that requires a specific sense, due to the nature of the check. For instance, if you're rolling Perception to "see what that thing is off on the ridge in the distance," that's likely a Perception check that requires sight. To roll perception to detect an invisible creature... that is probably not going to require sight, because you might be looking for their tracks or listening for them or smelling for them, etc. And even if something like looking for tracks is your only option (maybe you're in Silence?), you're sort of conflating being effectively Blinded in relation to the creature, vs. being actually Blinded as to the rest of your surroundings, like the tracks they might leave on the ground.
Invisibility, Concealment, Blinded, and Hiding are absolutely messy and somewhat contradictory systems, you're not wrong that there are some bizarre and unintended RAW pitfalls. But I don't think that there's a logical chain that requires that you automatically fail any perception check you make to find a hiding Invisible creature.
I agree with chickenchamp. Invisible doesn't mean silent. Other creatures can still hear you just fine. Some creatures have other very keen senses, like a mastiff (my pally rides one, so its the only one I know off the top of my head) which gets advantage on perception checks that use sound or smell (invisible doesn't cover your scent either).
Invis let’s you hide-at-will, even when you’re standing right in front of people. But it doesn’t give advantage on that roll, nor does it stop people from targeting you if you’re NOT hidden or haven’t beaten their Perception.
Invis and Silence, I give the above AND advantage to the roll. Or Invis and Boots of Elvenkind.
With Silence and Cloak of Elvenkind, I give advantage to the roll, but there’s no hide-at-will because you’re not invisible.
I also allow Silence to negate Heavy Armor penalties.
This considers sight and sound, the primary checks - vs a creature with smell benefits, I let them roll as normal. Basically, if you defeat two senses, I’ll give you advantage unless there’s some other special senses at play.
I'm excited by the thought of the auto-fail, but that is only in regards to those with regular sight (not truesight or blindsense or stuff like that.)
And those with special senses listed (hearing, smell etc.) can detect invisible creatures in those ways.
Now don't over-penalize the invisible condition either. To detect noise there has to be noise (someone in medium or heavy metal armor... or something else that clangs etc.) Those who wear less (clerices is robes or wizards in robes, rogues always try to be as silent as possible... a flying sprite?) Harder to disguise your smell or scent (but there might be ways?)
Anyway to detect something invisible you need these special senses in most cases as the regular senses aren't good enough... especially sight which auto-fails. (because invisible.)
Rollback Post to RevisionRollBack
"A rightful place awaits you in the Realms Above, in the Land of the Great Light. Come in peace, and live beneath the sun again, where trees and flowers grow."
— The message of Eilistraee to all decent drow.
"Run thy sword across my chains, Silver Lady, that I may join your dance.”
Now don't over-penalize the invisible condition either.
The condition is already very powerful as written. In my opinion it doesn't need any additional help from bending the rules.
To detect noise there has to be noise (someone in medium or heavy metal armor... or something else that clangs etc.) Those who wear less (clerices is robes or wizards in robes, rogues always try to be as silent as possible... a flying sprite?) Harder to disguise your smell or scent (but there might be ways?)
Everyone makes noise. I can hear my own footsteps walking around my house barefoot. Most player characters are going to be far noisier than that. Between the sheathe for their weapon, their coin purse, and the backpack they're likely carrying all of their tools, rations and loot in, it's going take deliberate effort to move quietly (which is precisely what the Hide action is supposed to represent.)
Anyway to detect something invisible you need these special senses in most cases as the regular senses aren't good enough... especially sight which auto-fails. (because invisible.)
You only need special senses to see the creature (mostly relevant for combat or targeting with non-area spells.) Like Chicken_Champ pointed out your other four senses are still applicable; that's why the rules specifically call out perception checks that rely on sight. And despite being unable to see the creature you might still be able to see signs of their presence (e.g. footprints in dust, mud or snow) even if they're perfectly quiet.
Invisibility basically boils down to being able to take the Hide action at will at like Brewsky said, immunity to being targeted by effects that require sight, and advantage/disadvantage on attack rolls (depending on who's on the receiving end.) And as far as hiding goes the rules are deliberately open-ended because hiding is highly situational. An invisible fighter dashing in full plate might have very little chance of avoiding notice in a quiet dungeon, yet effortlessly slip away in the chaos of an active battlefield.
Do creatures always know the exact location of creatures that are invisible, but not hidden?
The case for:
Invisible is not the same thing as invisible and hidden and giving too much to the former trivializes the latter.
The invisible condition in PHB Appendix A explains, “The [invisible] creature's location can be detected by any noise it makes or any tracks it leaves.”
PHB p177 says, “Signs of [an invisible creature] might still be noticed, and it does have to stay quiet.” Trying to avoid giving away tell-tale non-visual indicators of your location is done by taking the hide action.
In discussing stealth, Jeremy Crawford says, “It’s also perfectly in keeping with the rules for a group to assume that unless a person hides, people generally know where invisible people are in combat because of their movements, their sword swings, they are seeing the effect in the environment either because their weapon is clipping through bushes or they bumped up against a table as they walked by and they see the drinks wobble.” (starts 29:38)
The advantages of the invisible condition are the effects of the condition itself. The biggest benefit of being invisible is that it provides you with the conditions to hide continuously instead of having to find cover all the time. And when you do attempt to hide, the stealth check is often made at advantage due to being invisible.
If a creature is required to take the search action to perceive an invisible creature who is not hidden, then that invisible creature may as well be considered hidden as well.
The case against:
The rules use verbiage that is intentionally noncommittal when describing invisible creatures. Nothing in the rules or in JC’s interview explicitly states that invisible and unhidden creatures passively give away their position—only that it can or might happen.
PHB p177 says, “Signs of [an invisible creature] might still be noticed, and it does have to stay quiet,” but staying quiet can often be done simply by not doing things that make noise.
In the same discussion on stealth referenced above, Jeremy Crawford explains, “In some cases, a DM will decide that even an invisible [but not hidden] person's location is unknown to combatants because of the environment or the character's attentiveness... The DM might decide that the wizard who cast invisibility on herself, the orcs may have lost track of where she is.” (starts 28:42)
The Unseen Attackers section of chapter 9 of the Basic rules states, “When you attack a target that you can't see, you have disadvantage on the attack roll. This is true whether you're guessing the target's location or you're targeting a creature you can hear but not see. If the target isn't in the location you targeted, you automatically miss,” but how would you guess the wrong location if you knew exactly where the unseen attacker was?
The rogue Blindsense feature states, “Starting at 14th level, if you are able to hear, you are aware of the location of any hidden or invisible creature within 10 feet of you.”
The 18 level ranger Feral Senses feature states in part, “You are also aware of the location of any invisible creature within 30 feet of you, provided that the creature isn’t hidden from you, and you aren’t blinded or deafened.” If creatures know the location of invisible creatures automatically, then these features would not need to specify the ability to locate invisible creatures, and the usefulness of that aspect of those features would be negated.
The Rod of Alertness’ ability to “sense the location of any invisible hostile creature that is also in the bright light,” would not need to be pointed out if the location of invisible creatures was known by default.
Do creatures always know the exact location of creatures that are invisible, but not hidden?
This is the wrong question to ask because the rules distinguish between in combat and out of combat, so there's at least 2 contexts to consider:
In combat, most creatures stay alert for signs of danger all around, so if you come out of hiding and approach a creature, it usually sees you. However, under certain circumstances, the DM might allow you to stay hidden as you approach a creature that is distracted, allowing you to gain advantage on an attack roll before you are seen.
There's two implications here:
Outside of combat, creatures aren't necessarily alert.
In combat, they almost certainly are (unless the DM says otherwise), and you're expected to follow the hiding rules to escape their notice.
The case against:
PHB p177 says, “Signs of [an invisible creature] might still be noticed, and it does have to stay quiet,” but staying quiet can often be done simply by not doing things that make noise.
Right. Which is the argument for saying that situations may be such that a combatant who cannot see and cannot hear an enemy (perhaps because they’re 60 feet away and the enemy is in the middle of a 30’ fog cloud and there loud noise on the battlefield) should not know where that enemy is, because that situation is “basically” achieving the “unseen and unheard” condition that the PHB defines as Hiding.
Thats my whole point when arguing this. “Unseen and unheard” is what actually does the heavy lifting to remove your position from the enemy’s radar. Hiding is one way to become “unseen and unheard.” But there are others as well.
This conversation is helpful to me as a DM because I will soon have my group fight an invisible stalker. I was not quite sure how I was going to handle their ability to target it. In theory the invisible stalker could move in, make a melee attack, and move away to any point on the battlefield and they would have to somehow guess how to target it. I wasn't sure how they were going to handle it, short of having someone hit it with a faerie fire spell or something. Was thinking if they just "guess a spot" and attack it, and hope they hit, it's way too random. They could hold their action to make an attack as soon as they are attacked I guess, would still be at disadvantage but at least they know where to target.
Mostly I am trying to walk the line between it being a unique challenge, but not being so difficult to hit, that it becomes tedious. Turn after turn of miss, miss, miss will not be fun for anyone... I think I will probably bend the rules and let them take the "Search" action as a bonus action for just this battle. The idea being that they are constantly trying to search for the enemy the entire battle, so based on the information they have gathered in prior rounds it only takes a bonus action. That way depending on how well they roll for perception, they can get a more precise idea where it is the better they roll (could be a specific spot or just "somewhere to the north"). Narratively I guess an invisible stalker can fly/hover, so no footprints to track, but would still make sounds moving across the area, making attacks, maybe kicking up dust, etc.
This conversation is helpful to me as a DM because I will soon have my group fight an invisible stalker. I was not quite sure how I was going to handle their ability to target it. In theory the invisible stalker could move in, make a melee attack, and move away to any point on the battlefield and they would have to somehow guess how to target it. I wasn't sure how they were going to handle it, short of having someone hit it with a faerie fire spell or something. Was thinking if they just "guess a spot" and attack it, and hope they hit, it's way too random. They could hold their action to make an attack as soon as they are attacked I guess, would still be at disadvantage but at least they know where to target.
Mostly I am trying to walk the line between it being a unique challenge, but not being so difficult to hit, that it becomes tedious. Turn after turn of miss, miss, miss will not be fun for anyone... I think I will probably bend the rules and let them take the "Search" action as a bonus action for just this battle. The idea being that they are constantly trying to search for the enemy the entire battle, so based on the information they have gathered in prior rounds it only takes a bonus action. That way depending on how well they roll for perception, they can get a more precise idea where it is the better they roll (could be a specific spot or just "somewhere to the north"). Narratively I guess an invisible stalker can fly/hover, so no footprints to track, but would still make sounds moving across the area, making attacks, maybe kicking up dust, etc.
If you play invisible being un-targetable and requiring people to guess the location, Invisible Stalkers just became the most OP summon in the game. Unless you enemy has See Invis or some other form of special senses, Invis Stalkers will literally obliterate everything in their path. They are immune to Opp Attacks and most spells, have Advantage on every attack, and Disadvantage to hit them *even if you manage to guess where they are*. Because you can move with impunity, you can go literally anywhere on the battlefield.
This is one of those things where it might be fun to play it this way versus the players to scare them, but if you play that way and renege later when they use it on your monsters… you’re going to have a bad time.
If you play them where they are targetable while invisible, it’ll be much more playable.
In most cases involving an invisible Sprite there would be no footprints due to the Sprite flying and how much noise is this Sprite making... for that matter even the scent or smell from a Sprite would be negligible.
In the original post, I posted the rules for Invisibility and heavily obscured and blinded because there was a section in each that I was referencing... I'm not excluding that there are ways to detect invisible things, just that in most cases if they are not there then you can't have an auto-fallback.
Like if there are muddy footprints then you can follow them to the last one and find the invisible creature that way, but if there are no footprints then you can't detect an invisible creature that way.
And i don't think that if you're not hidden then you are automatically revealed.
The whole point of being invisible is to go undetected. People would watch where they step and move quietly.
In the example of a flying invisible Sprite I would say they are nigh impossible to detect.
And in closing this post I just want to mention that I wasn't aware of how these rules interacted before and just wanted to see if anyone else was aware of the auto-fail. The auto-fail I'm referring to is: When someone is invisible they are considered to be heavily obscured (in both cases you cannot see 100% of the creature.) For purposes of seeing an invisible creature (without aid of magic, or special sight(truevision) or senses(keen senses, blindsense)) the observer is considered to be under the Blinded condition, but just in relation to trying to see the invisible creature. And finally, the Blinded condition states that they auto-fail any ability checks that require sight to detect the invisible creature..
So I guess where the auto-fail comes in for my example of an invisible flying Sprite is... no footprints, negligible sound and smell... you're mainly left with sight to try and detect the Sprite. Unless you're lucky enough to have some other means of detection.
Like some have mentioned already, each DM will have to deal with each case individually as there will be a myriad of things that affect the ruling.
One last thing to consider, even without hiding, someone who is invisible should be hard to detect not easy. Incidental sounds and smells don't usually work unless you have a keen sense or something similar. The mention of parts of the podcast like someone invisible accidentally bumping into a table... when you're not invisible how often do you bump into a table, and being invisible wouldn't you be extra careful not to bump into anything, I know I would. Smells blend into the background for the most part unless they particularly strong or ripe, and again since we don't often use our sense of smell like those animals with keen senses who have a sense of smell that is 100 or 1,000 times stronger than ours, using it to detect invisible doesn't seem that plausible to me.
Rollback Post to RevisionRollBack
"A rightful place awaits you in the Realms Above, in the Land of the Great Light. Come in peace, and live beneath the sun again, where trees and flowers grow."
— The message of Eilistraee to all decent drow.
"Run thy sword across my chains, Silver Lady, that I may join your dance.”
— A basic prayer.
To post a comment, please login or register a new account.
Invisible
So you need magic or special senses, or the invisible creature needs to make noise or leave tracks. (I would imagine an invisible flying Sprite leaves no tracks and makes very little noise.) The one thing I find very interesting here is that for the purpose of hiding the creature is considered heavily obscured.
A heavily obscured area—such as darkness, opaque fog, or dense foliage—blocks vision entirely. A creature effectively suffers from the blinded condition when trying to see something in that area.
So, 1. If something is invisible treat it as trying to see in heavy obscured conditions. And, 2. A creature suffers the blinded condition trying to see something in that area.
Blinded
So, Invisible = Heavily Obscured. And Heavily Obscured = Blinded. And Blinded = auto fails any ability checks that require sight... like the Perception check (passive or not) made to detect an hidden invisible creature. (like a Sprite with +8 to Stealth)
I mean having disadvantage to find such a creature is one thing but to have anyone auto fail when trying to find the hidden invisible Sprite is really cool.)
What you're glossing over is that you automatically fail an ability check that "requires sight," and only in relation to that Invisible creature itself.
That "requires (sense)" terminology is something that 5E uses in a lot of different places. See various monsters with Keen Senses like a Wolf, or an Owl, or things like Sunlight Sensitivity on a Drow. To some extent, Perception always uses all of your senses, but a specific Perception check might be asked for that requires a specific sense, due to the nature of the check. For instance, if you're rolling Perception to "see what that thing is off on the ridge in the distance," that's likely a Perception check that requires sight. To roll perception to detect an invisible creature... that is probably not going to require sight, because you might be looking for their tracks or listening for them or smelling for them, etc. And even if something like looking for tracks is your only option (maybe you're in Silence?), you're sort of conflating being effectively Blinded in relation to the creature, vs. being actually Blinded as to the rest of your surroundings, like the tracks they might leave on the ground.
Invisibility, Concealment, Blinded, and Hiding are absolutely messy and somewhat contradictory systems, you're not wrong that there are some bizarre and unintended RAW pitfalls. But I don't think that there's a logical chain that requires that you automatically fail any perception check you make to find a hiding Invisible creature.
dndbeyond.com forum tags
I'm going to make this way harder than it needs to be.
I agree with chickenchamp. Invisible doesn't mean silent. Other creatures can still hear you just fine. Some creatures have other very keen senses, like a mastiff (my pally rides one, so its the only one I know off the top of my head) which gets advantage on perception checks that use sound or smell (invisible doesn't cover your scent either).
Here’s how I play it:
Invis let’s you hide-at-will, even when you’re standing right in front of people. But it doesn’t give advantage on that roll, nor does it stop people from targeting you if you’re NOT hidden or haven’t beaten their Perception.
Invis and Silence, I give the above AND advantage to the roll. Or Invis and Boots of Elvenkind.
With Silence and Cloak of Elvenkind, I give advantage to the roll, but there’s no hide-at-will because you’re not invisible.
I also allow Silence to negate Heavy Armor penalties.
This considers sight and sound, the primary checks - vs a creature with smell benefits, I let them roll as normal. Basically, if you defeat two senses, I’ll give you advantage unless there’s some other special senses at play.
I'm excited by the thought of the auto-fail, but that is only in regards to those with regular sight (not truesight or blindsense or stuff like that.)
And those with special senses listed (hearing, smell etc.) can detect invisible creatures in those ways.
Now don't over-penalize the invisible condition either. To detect noise there has to be noise (someone in medium or heavy metal armor... or something else that clangs etc.) Those who wear less (clerices is robes or wizards in robes, rogues always try to be as silent as possible... a flying sprite?) Harder to disguise your smell or scent (but there might be ways?)
Anyway to detect something invisible you need these special senses in most cases as the regular senses aren't good enough... especially sight which auto-fails. (because invisible.)
The condition is already very powerful as written. In my opinion it doesn't need any additional help from bending the rules.
Everyone makes noise. I can hear my own footsteps walking around my house barefoot. Most player characters are going to be far noisier than that. Between the sheathe for their weapon, their coin purse, and the backpack they're likely carrying all of their tools, rations and loot in, it's going take deliberate effort to move quietly (which is precisely what the Hide action is supposed to represent.)
You only need special senses to see the creature (mostly relevant for combat or targeting with non-area spells.) Like Chicken_Champ pointed out your other four senses are still applicable; that's why the rules specifically call out perception checks that rely on sight. And despite being unable to see the creature you might still be able to see signs of their presence (e.g. footprints in dust, mud or snow) even if they're perfectly quiet.
Invisibility basically boils down to being able to take the Hide action at will at like Brewsky said, immunity to being targeted by effects that require sight, and advantage/disadvantage on attack rolls (depending on who's on the receiving end.) And as far as hiding goes the rules are deliberately open-ended because hiding is highly situational. An invisible fighter dashing in full plate might have very little chance of avoiding notice in a quiet dungeon, yet effortlessly slip away in the chaos of an active battlefield.
The Forum Infestation (TM)
Do creatures always know the exact location of creatures that are invisible, but not hidden?
The case for:
The case against:
"Not all those who wander are lost"
This is the wrong question to ask because the rules distinguish between in combat and out of combat, so there's at least 2 contexts to consider:
There's two implications here:
This is basically what hiding is though.
The Forum Infestation (TM)
Right. Which is the argument for saying that situations may be such that a combatant who cannot see and cannot hear an enemy (perhaps because they’re 60 feet away and the enemy is in the middle of a 30’ fog cloud and there loud noise on the battlefield) should not know where that enemy is, because that situation is “basically” achieving the “unseen and unheard” condition that the PHB defines as Hiding.
Thats my whole point when arguing this. “Unseen and unheard” is what actually does the heavy lifting to remove your position from the enemy’s radar. Hiding is one way to become “unseen and unheard.” But there are others as well.
dndbeyond.com forum tags
I'm going to make this way harder than it needs to be.
This conversation is helpful to me as a DM because I will soon have my group fight an invisible stalker. I was not quite sure how I was going to handle their ability to target it. In theory the invisible stalker could move in, make a melee attack, and move away to any point on the battlefield and they would have to somehow guess how to target it. I wasn't sure how they were going to handle it, short of having someone hit it with a faerie fire spell or something. Was thinking if they just "guess a spot" and attack it, and hope they hit, it's way too random. They could hold their action to make an attack as soon as they are attacked I guess, would still be at disadvantage but at least they know where to target.
Mostly I am trying to walk the line between it being a unique challenge, but not being so difficult to hit, that it becomes tedious. Turn after turn of miss, miss, miss will not be fun for anyone... I think I will probably bend the rules and let them take the "Search" action as a bonus action for just this battle. The idea being that they are constantly trying to search for the enemy the entire battle, so based on the information they have gathered in prior rounds it only takes a bonus action. That way depending on how well they roll for perception, they can get a more precise idea where it is the better they roll (could be a specific spot or just "somewhere to the north"). Narratively I guess an invisible stalker can fly/hover, so no footprints to track, but would still make sounds moving across the area, making attacks, maybe kicking up dust, etc.
If you play invisible being un-targetable and requiring people to guess the location, Invisible Stalkers just became the most OP summon in the game. Unless you enemy has See Invis or some other form of special senses, Invis Stalkers will literally obliterate everything in their path. They are immune to Opp Attacks and most spells, have Advantage on every attack, and Disadvantage to hit them *even if you manage to guess where they are*. Because you can move with impunity, you can go literally anywhere on the battlefield.
This is one of those things where it might be fun to play it this way versus the players to scare them, but if you play that way and renege later when they use it on your monsters… you’re going to have a bad time.
If you play them where they are targetable while invisible, it’ll be much more playable.
Agreed.
In most cases involving an invisible Sprite there would be no footprints due to the Sprite flying and how much noise is this Sprite making... for that matter even the scent or smell from a Sprite would be negligible.
In the original post, I posted the rules for Invisibility and heavily obscured and blinded because there was a section in each that I was referencing... I'm not excluding that there are ways to detect invisible things, just that in most cases if they are not there then you can't have an auto-fallback.
Like if there are muddy footprints then you can follow them to the last one and find the invisible creature that way, but if there are no footprints then you can't detect an invisible creature that way.
And i don't think that if you're not hidden then you are automatically revealed.
The whole point of being invisible is to go undetected. People would watch where they step and move quietly.
In the example of a flying invisible Sprite I would say they are nigh impossible to detect.
And in closing this post I just want to mention that I wasn't aware of how these rules interacted before and just wanted to see if anyone else was aware of the auto-fail.
The auto-fail I'm referring to is: When someone is invisible they are considered to be heavily obscured (in both cases you cannot see 100% of the creature.)
For purposes of seeing an invisible creature (without aid of magic, or special sight(truevision) or senses(keen senses, blindsense)) the observer is considered to be under the Blinded condition, but just in relation to trying to see the invisible creature.
And finally, the Blinded condition states that they auto-fail any ability checks that require sight to detect the invisible creature..
So I guess where the auto-fail comes in for my example of an invisible flying Sprite is... no footprints, negligible sound and smell... you're mainly left with sight to try and detect the Sprite. Unless you're lucky enough to have some other means of detection.
Like some have mentioned already, each DM will have to deal with each case individually as there will be a myriad of things that affect the ruling.
One last thing to consider, even without hiding, someone who is invisible should be hard to detect not easy.
Incidental sounds and smells don't usually work unless you have a keen sense or something similar. The mention of parts of the podcast like someone invisible accidentally bumping into a table... when you're not invisible how often do you bump into a table, and being invisible wouldn't you be extra careful not to bump into anything, I know I would. Smells blend into the background for the most part unless they particularly strong or ripe, and again since we don't often use our sense of smell like those animals with keen senses who have a sense of smell that is 100 or 1,000 times stronger than ours, using it to detect invisible doesn't seem that plausible to me.