Sacrifice (5e Feat)
From D&D Wiki
Prerequisites: Constitution 15, You must have taken damage from a demon
Your conflicts with demons have left you branded, in turn making you supernaturally aware of the supernatural. You are aware of any fiends, celestials, monstrosities, undead, and aberrations that come within 200 feet of you, but not their location. If a CR 17+ creature of any of the aforementioned types comes within 200 feet of you, and again within 100 and 30 feet, you loose 1 hit point as the brand begins to bleed. This damage can not reduce your hit points below 10 hit points. Each creature can only deal this damage once per listed distance.