MDT-1B 1-channel Block Coded Visor Transmitter Compatible with all Linear access receivers and controllers. Superior transmission range. Factory programmed MegaCode format supports over 1,000,000 codes. Unique "Extra" top button. High visibility operate LED. Visor clip included. Two type 2032 lithium batteries supplied. MegaCode format. RF frequency: 318 MHz. The Model MDT-1B 1-channel Block Coded Visor Transmitter is designed for use with Linear's access control products. The Model MDT-1B is a single-channel device. Pressing either the round button on the transmitter's front, or the small button on the transmitter's top will send the same signal. 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