Here's what other sites are saying:
The Pieps Backup Transmitter is there for when you need added safety. This Backup transmitter is worn along with your other beacon just in case your main beacon is separated from you.
Black Diamond Pieps Backup Avalanche Transmitter - Black Diamond Pieps Backup Avalanche Rescue Transmitter, lightweight, durable, and worn directly on your body. The Pieps Backup Avalanche Transmitter transits only in an emergency and automatically goes into transmit mode when separated from your main beacon by more than one meter!
Worn directly on your body along with your main beacon, the PIEPS Backup Avalanche Transmitter automatically goes into transmit mode when separated from your main beacon by more than one meter, providing the only complete solution against secondary avalanches.
- Black Diamond Equipment
The Pieps Backup Transmitter is designed to be worn with your avalanche beacon, and provides a backup if you're searching for a victim after a slide and get caught in a secondary avalanche and separated from your beacon by more than a meter. Once the device senses you're no longer in motion, it goes into transmit mode. This is a backup device only, and not intended to be used instead of an avalanche beacon.
Features of the Black Diamond PIEPS Backup Transmitter Compatible with any standard (457 kHz) beacon on the market Accelerometer keeps Backup from transmitting when still in motion 1 Alkaline AAA battery IEC-LR03, 1.5V