The Model MDT-4B 5-channel Block Coded Visor Transmitter is designed for use with Linear's access control products. The Model MDT-4B is five-channel device. Pressing one of the transmitter's front buttons sends channel one through four. Pressing the small button on the transmitter's top sends channel five. The top button can be hidden with the top button cover supplied. Also included are lithium batteries with a five-year service life and a visor clip. 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.