Transmitter activates wireless security system's alarm with the press of a button. With a Weatherproof Transmitter, a child or elderly parent will be able to keep handy a device that will sound the SecureLinc's 85dB alarm at the press of a button. The SecureLinc II Wireless Security System is sold separately.This miniature pendant UHF transmitter can be worn around the neck or on a keychain; both a neck chain and key ring are included. To activate the transmission, just depress the button, which will send out a 24-bit ID code and an alarm code, which the SecureLinc can identify.The transmitter is completely weatherproof and can even be worn in the shower. An unlimited number of pendant transmitters can trigger the system. more info