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. Using the Signature Series Sound Monitor Transmitter, you can be notified of sounds around the home. The Sidekick II Receiver will flash when it has been activated. Includes 2 AA batteries. Five year warranty. Features: Picks up sounds 3/4 of a second or more in length 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.