Detect Heat

For the duration, you see differences in temperature within 30 feet of you. Hotter surfaces appear red and colder surfaces appear blue. You get advantage on all perception checks relying on sight targeted towards endothermic creatures.  

The spell can penetrate most barriers, but it is blocked by 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood or dirt.