I carry a tone probe in my tool bag for troubleshooting Ethernet wiring. It's got a pushbutton on switch. Sometimes it would move around in my bag and the button would activate, killing the battery. 

I was using it today and before putting it back in the bag, I decided to design and make a snap-on sliding cover for the button. I made it snug enough to where it still slides, but not so easily that it moves by itself from the closed position. Every tone probe I've owned seems to basically be the same form and size, so this may work well for other models with minor scaling changes.