We got this to evaluate the cleanliness of the carpet in a house we bought, whose previous owners had a dog.
All you have to do is wait until dark, turn out the lights, and shine it on the carpet. In the case of the room we looked at, 75 urine spots scattered throughout the room, spots on top of spots, and this after “cleaning”. We ended up replacing the carpet.
So before buying this you must ask yourself, “the urine may be there, but do I really want to know if it is?” Because this will tell you, and you might not like the answer.