Monitors audio activity over a wide range of input voltages- Two sets of C-form both N.O and N.C relay contacts respond to audio activity- Four levels of signals: microphone, 600-ohm line, 25V, and 70V speaker systems- Built-in balanced, low noise, high gain microphone pre-am- Transformer-isolated, 600-ohm small signal level output of detected audio available- Works with self-amplified or central-amplified paging systems- Separate microphone pre-amp gain control- Adjustable release delay: 0.25s to 25s- Trigger threshold adjustment- Relay active indicator light- Accessories: PRS40C 12V DC Power Supply Sold separately