The Model ACT-21B 1-Channel Block Coded Key Ring Transmitter is designed for use with Linear’s access control products. The Model ACT-21B is a single-channel device supplied with a quick-disconnect key ring. Also included are lithium batteries with a five-year service life. A unique 10-second time-out feature prevents the system from being shut down by a single transmitter transmitting continuously. The transmitter is MegaCode format, which means each transmitter is factory preprogrammed with one of over 1,000,000 codes, virtually eliminating the possibility of code duplication. Because the receiver ”learns” each specific code, no unauthorized person can gain access to the system by reprogramming a transmitter. Block coded transmitters are factory programmed to a sequential series of transmitter ID codes. When used with a Linear access controller, transmitters can be locally or remotely programmed into memory by entering the first and last codes of the block into the system. Facility codes can be selected to further customize the system.