Even a hint of cat urine odor makes most people want to run away from home, and once it dries, it's nearly invisible to the eyes. If you can smell it but can't see it, a black light will locate the source of the odor for you.
Narrow down your search by using your eyes and nose. Even old cat urine has a strong, distinguishable ammonia odor.
Turn out all the lights in the room where you suspect the urine spot is located. If it is daylight outside, close your blinds or cover your windows temporarily with sheets.
Plug in the black light, turn it on and slowly work your way around the room. Do not forget to check on and behind furniture and under items on the floor. Older stains will glow pale yellow, while fresh spots will be brighter.
Use a sweeping motion with the blacklight and make sure you cover the entire room. Do not stop when you find one stain. It is not unusual for multiple urine spots to exist in the same room.
Check baseboards, walls, bookshelves and other surfaces, especially if you have a cat known for spraying.
Mark any urine spots with a piece of masking tape so you can find them later. Place tape on all sides of the urine spots to ensure you clean the entire area.
Sandra Ketcham has nearly two decades of experience writing and editing for major websites and magazines. Her work appears in numerous web and print publications, including "The Atlanta Journal-Constitution," "The Tampa Bay Times," Visit Florida, "USA Today," AOL's Gadling and "Kraze Magazine."