A cross between short-distance radio communication and the Message cantrip, the A016 Tactical Earpiece allows the wearer to communicate with others on the same frequency. While wearing the earpiece, you may enable or disable active transmission as a bonus action. While enabled, all creatures on the same plane as you within 1000ft can hear anything you say, as well as a certain level of background noise, provided they are also equipped with a radio receiver tuned to the same frequency. 

Magical silence, antimagic, 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood blocks communication. The transmission doesn't have to follow a straight line and can travel freely around corners or through openings.