When the Sidekick Receiver receives a signal from any Silent Call transmitter placed within 100 feet, the strobe light will be activated and flash for 15 seconds. A light also shines below the symbol(s) indicating which transmitter sent the signal. The alerting device has a doorbell transmitter that will send a signal to your Sidekick Receiver when your existing doorbell button is pressed. When the telephone/TTY rings, the transmitter sends a signal to your Sidekick Receiver. The diverse and expandable setup can be used with optional bed vibrator (sold separately) and you may add or remove transmitters as desired to best suit your needs.