MCT-3 megacode garage door opener 318 mhz transmitter, no dip switches to set MegaCode transmitters and receivers do not contain a typical ""coding switch"". Each of the three transmitter buttons will send a unique code when pressed. One button can be used to activate your garage door opener, a second button can operate an access gate, a third button can activate an additional garage door operator or most Linear 318 MHz MegaCode wireless receivers. The receiver is programmed by learning a transmitter's unique digital code. The receiver will activate only from the memorized transmitters. It has a high visibility test/operate LED A spring-steel, dual-position visor clip that attaches vertically or horizontally. It measures 3.04-by-1.93-by-.61 inches. It is available for use with all Linear?s garage door openers. The transmitter is powered by two Type CR2032 coin-cell batteries.