When my older cat started peeing in spots other than her litter box in her older age, I ordered UV lights from Amazon to find new spots she found to pee. (My sweet baby was respectful enough to only pee on the tile instead of my carpet.) The cheap Amazon flashlights only worked in the dark and her pee spots were revealed.
Fast forward several months...my baby passed away, and my friend from Cali advertised his PP5000. I was slightly intrigued since I wanted to show off how disgusting our work furniture may be. Anyway, once it arrived in the mail, I charged the batteries and shone the light around my house and...holy sh**! I had no idea that my cleaning methods were lacking so much. My carpet looks perfect from the naked eye, and my Bissel Crosswave seemed to clean very well. Well...after shining the PP5000 around the house, I learned that every. single. spot. was still showing up under the UV light. I even picked up spots where she threw up several years ago! That is nuts! This is a very powerful UV light and it will pick up anything you want, or DON'T want to see. Highly recommended! The extra $ is totally worth it!
P.S.-Brian Sapp's review is worthless.