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.