This seems like a very useful spell and this would end robbing forever but I am new to d&d so I don't know where to get stuff like the things needed.

This spell is showing up in my character sheet as a "cast at higher levels" spell, but I'm not seeing a higher level cast effect here.

unless your bag is larger than 20 cubic feet, you should be able to.

Quote from Tradyk >>

Only if you didn't move your backpack. 

 Nope. You could move your backpack.

does alarm work on ethereal creatures such as ghosts

That's to say you can cast it with a higher slot if you wanted to

If someone dispels an Active Alarm successfully, is the caster of the Alarm aware that the spell has ended prematurely?

Is the range referring to how far away from you the area can be when you cast or do you have to stay inside that area while it is active?  i.e. if I cast it on the door to my room at the local inn and then go shopping, will I still feel that ping when someone goes in my room and I am across town?

play however you wish but if i were a DM i would say that you could cast it on an enclosed space that could then be moved

What is the maximum size of the Alarm spell?
It states that the area is a max of "a 20 foot cube" so is it that
1. The max size is exactly 20x20x20. and you can either ward a door. window or that space exactly
2. that is the max size in any dimension such as if you did 5x5, max vertical is still 20.
3. that is the maximum volume not area so you can change the dimensions at will so the maximum linear feet is 8,000. so you could do a 15X15x35

4. or is it that if you aren't warding an entrance is it that it has to be a cube and the maximum cube size is 20x20x20

Quote from Lazythor >>

What is the maximum size of the Alarm spell?
It states that the area is a max of "a 20 foot cube" so is it that
1. The max size is exactly 20x20x20. and you can either ward a door. window or that space exactly
2. that is the max size in any dimension such as if you did 5x5, max vertical is still 20.
3. that is the maximum volume not area so you can change the dimensions at will so the maximum linear feet is 8,000. so you could do a 15X15x35

4. or is it that if you aren't warding an entrance is it that it has to be a cube and the maximum cube size is 20x20x20

 My reading is that the spell gives you three possible targets:

1. One door (no size limit)
2. One window (no size limit)
3. An area of any shape that fits inside a 20x20x20 ft cube.

So close to option 4 except that the area doesn't strictly have to be cube-shaped. I admit the exact meaning of "is no larger than" is open to interpretation though; it could mean "is no longer in any dimension than" or "has a volume no greater than". I favour the former to avoid shenanigans with choosing an area miles long but the thickness of a human hair, but if you also interpret "an area within range" to mean that the entire area has to be within range, that limits it to being 60 feet long anyway.

So as always, discuss it with your DM to be sure. :)

Quote from Tesseract_ >>

There's nothing in the rules about how relativity applies to spell areas of effect. It's the DM's call.

Quote from littlegreentree >>

Nothing in the description text leads me to believe you couldn't put it on an object that was in motion, stopped, and continued to be in motion. Because in the spell description nothing is specific about the location or its relative movement so I would think you'd be able to place it on an object or an area that was in motion ie a cart or literally a backpack on your person. Right?

 The rules on Area of Effect state "Every area of effect has a point of origin, a location from which the spell's energy erupts. The rules for each shape specify how you position its point of origin. Typically, a point of origin is a point in space, but some spells have an area whose origin is a creature or an object." So when you choose an area, it applies to that point in space, not fixed to an objects RAW.

It doesn't say anything about how hard it is to detect if an alarm spell is present in an area. Is there an investigation DC associated with noticing the ward? My players decided to do some B&E and I expect the owner would protect a location with this spell. Is the spell designed to be undetectable so they have no chance to save against the ward or do they at least have a chance to avoid it? 

I want to be sure I rule this correctly now in case my players want to start using this spell for themselves. If they can detect it and/or dispel it then so can their enemies. 

It doesn't say anything about how hard it is to detect if an alarm spell is present in an area. Is there an investigation DC associated with noticing the ward? My players decided to do some B&E and I expect the owner would protect a location with this spell. Is the spell designed to be undetectable so they have no chance to save against the ward or do they at least have a chance to avoid it? 

I want to be sure I rule this correctly now in case my players want to start using this spell for themselves. If they can detect it and/or dispel it then so can their enemies. 

Hi! As it doesn't say, I would deem this as up to the DM on how they want to rule it. You could either say that the spell is invisible to any eye except the caster once its been put in place. I'd personally probably go this route myself, but if you want the option for it to be detected, you could rule it that the person seeking any traps or otherwise has to roll Investigation/Perception against the caster's spell save DC.

Also, don't forget about Detect Magic. That should pick it up.

bru

Just to make sure my understanding is correct or at least commonly agreed upon, if a creature was on the astral plane and the alarm on the material it would not trigger the alarm as it entered the area of the spell but it would when shifting to the material plane and "touching" the area? 

Just to confirm a paladin that has chosen the Oath of the Watchers can also ritual cast this spell correct?

Would someone get a chance to detect this?  Maybe with an Investigation check with a DC set by the caster's spell save?

I fully agree that it says "no larger  than a 20ft cube" but this is surely a mistake. To go from a doorway or window and then to 8000 cubic feet is disproportionate. Did they not mean 20 cubic feet.

It gets even sillier when you consider there is no ruling that you cannot have numerous castings running at the same time and as you can cast it as a ritual and not be limited by spell slots you can alarm a truly ridiculous area.