I bought a piece of 1.5 inch stiff foam to try to fix a sag in a bed. It didn't work but having that thick piece of solid foam around has been a life saver.
Need something flat to put a laptop on? Throw it on the foam. Going to be doing something that requires you to be on your knees for a while? Get the foam!
It went from stupid purchase to something I'd gladly replace if it broke.
I bought a house with these and didn't realize it had this feature for like a year (batteries had died). Now I love it. I find myself taping every faucet it use and am annoyed when others don't turn on.
I actually bought a handfree soap dispenser to go next to it, which is a great combo. Preparing meat or something, I can clean my hands and tap sink with elbow and not worry about cross contamination of everything.