The new 418MHz Signature Series uses radio frequency technology, allowing you freedom and flexibility with outstanding features and increased range of up to 2,000 feet. Quickly know when you have visitors, telephone calls or emergencies with the bright flashing strobe and distinctive LEDs. Connect this transmitter to your telephone, TTY or VP (videophone). When you receive an incoming call, it will transmit to the Sidekick II Strobe Receiver that will flash to notify you. Includes 2 AA batteries and dual phone jack. Five year warranty. Features: Range up to 2,000 feet Low battery indicator What else do I need to make this work? This product will only work with 418MHz products in the Silent Call Signature Series. In order to be notified, you will need to purchase a Silent Call Signature Series Receiver.