Old Sock Tester
We all know how battery testers work: you find a battery in your home or office and have no clue if it's still usable. You attach it to a battery tester and voila - the battery is flat so you can happily dispose of it.
But on washing day, what are you to do if you find a couple of stray socks? Sure, you can smell every single one of them, but that isn't only unpleasant, but it can actually damage your health, e.g. if you're allergic to dust. Alternatively, you can throw everything you find into the washer, but that'll unnecessarily shorten the life-span of your clothers, plus, by washing stuff that's already clean you're not exactly doing a favor to our environment.
This is where the sock tester comes to play: scan the socks (or any other garment you may have found) with the sock tester, and the sock tester will tell you if they actually need a washing.
Reward: Free sock testers for me