RollQuest summary of the SRD 5.1 rules, not a quotation.
As an action, until the end of your next turn you know the location of any celestial, fiend, or undead within 60 ft of you that is not behind total cover, and you know its type but not its identity. Within the same radius you also detect the presence of any place or object that has been consecrated or desecrated, as with the hallow spell. Uses = 1 + CHA mod, and you regain all expended uses when you finish a long rest.
RollQuest ships the D&D 2014 SRD as a content pack, on a 5e character sheet that does the maths - roll from the sheet and let the numbers work themselves out. Free to start.