Bloodsight

You draw out a portion of your blood, causing your eyes to take on a crimson hue. For the duration, you can see the life force of nearby creatures. The range of this vision is a number of feet equal to 5 times the number of hit points spent on this spell. When a creature is at full health, they appear perfectly normal, but as they become more wounded a red aura begins to surround them. You can notice when a creature's current hit points are below 1/2 or 1/4 of their hit point maximum. If a creature is below 1/2 of their hit point maximum, you can see them even through walls and invisibility. 

At Higher Levels. If you cast this spell using a spell slot of 5th level or higher the duration is 1 hour. If you use a slot of 7th level or higher, the duration is 8 hours. If you use a 9th level spell slot, the duration is 24 hours. Using a spell slot of 5th level or higher grants a duration that doesn't require concentration.