Voice-Activated Relay. 2 sets of C-Form (N.O. and N.C.) relay contacts respond to audio activity. 4 levels of input signals: microphone, 600-ohm line, 25V, and 70V speaker systems. Built-in balanced, low noise, high gain microphone pre-amp. A transformer-isolated, 600-ohm small signal level output of detected audio available. Trigger threshold adjustment.