On the power pack of the CM311A are two switches. One (a slider) turns the powerpack on and off. The other (a push button) can be set to do one of a couple of things, but I configured mine to MUTE the mic. On the top of the powerpack is a red LED light which indicates when the mic is live...and turns off when when the mic is muted. This feature is very convenient should you feel a cough, sneeze, etc coming on...or when someone comes up to talk to you while you are wearing it.

Eddie