Mini-Vox and Relay Kit (Kit) The idea behind a VOX (voice activated switch) is that instead of the user pressing a switch to activate a relay, the sound of the users voice itself activates the relay. This gives hands-free control over devices like tape recorders. Power supply needed: 12VDC center positive 2.5mm jack. Electret microphone to pick up the sound is included. Skill Level : Kit - Basic Soldering Required