The Model MDT-1A 1-Channel Visor Transmitter is designed for use with Linear’s access control products. The Model MDT-1A 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.