I remember them on mp3-Player, Walkmans, Microphones and even Mobile-Phones. Usually on device that you want to lock or particularly turn on and off. And someti

I remember them on mp3-Player, Walkmans, Microphones and even Mobile-Phones. Usually on device that you want to lock or particularly turn on and off. And sometimes you have to push them hard with the help of your Fingernail.