The Model MDT-2A 3-channel Visor Transmitter is designed for use with Linear's access control products. The Model MDT-2A is a three-channel device. Pressing the transmitter's left or right front button sends channel one or two. Pressing the small button on the transmitter's top sends channel three. 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.