You are probably looking for Optogate Automatic Microphone switches. 

These units act as proximity sensor vocal mute accessory instead of a push to mute . 

Check out the image to get a better view of how it’s set up. 

This page was created to help guide you toward the optical infrared automatic microphone switch device you are looking for. 

Optagate.com will automatically redirect you to The primary distributor for Canada , United States, Central American , and South American of Optogate laser microphone noise gates. 

Optagate mutes the microphone so you don’t have to . It is most useful for serious audio engineers responsible for the sonic improvements to live sound performances. 

Church or Entertainment Music Directors, Front of House, Monitor engineers, audio engineers, playback engineers, musicians, and the audience will notice the live sound mix be much cleaner with greater sound clarity.