If you have mild to severe hearing loss, make sure you always know when your baby is crying with the Sonic Alert BC400 Baby Cry Signaler/Transmitter. This small voice sensor plugs into an outlet in your babys room and detects even the softest coo. When any crying is detected, the signaler lets you know by sending a wireless alert to your Sonic Alert receiver (sold separately), which flashes a light upon activation. The signaler does not flash or make noise itself, ensuring your baby is undisturbed by the system. The Baby Cry Signaler/Transmitter features adjustable sensitivity, so you can choose to detect all baby sounds, quiet and loud (high sensitivity), or only louder sounds (low sensitivity). Make adjustments simply by turning a knob on the signaler. COMPATIBLE RECEIVERS: Boom Alarm Clock (SB1000), Wall Mount Remote Receiver (SA101), Table Top Remote Receiver (SA201), Sonic Blink Strobe Receiver (BL300), Remote Horn Receiver (RH100). NOTE: Requires a compatible Sonic Alert receiver, sold separately.