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The system typically features three buttons, most often found on the driver-side visor or on the overhead console, which can be programmed via a training sequence to replace existing remote controls. It is compatible with most RF-controlled garage door openers, as well as home automation systems such as those based on the X10 protocol.
Simple remote control systems use a fixed code word; the code word that opens the gate today will also open the gate tomorrow. An attacker with an appropriate receiver could discover the code word and use it to gain access sometime later. More sophisticated remote control systems use a rolling code (or hopping code) that changes for every use.
Rolling code technology is also used on car remote controls and with some internet protocols for secure sites. The fourth stage of garage door opener systems is similar to third stage, but it is limited to the 315 MHz frequency. The 315 MHz frequency range avoids interference from the land mobile radio system (LMRS) used by the U.S. military.
Chamberlain, LiftMaster, and Craftsman have interchangeable parts, primarily the gear and circuit boards. The greatest difference between the brands is that Chamberlain and Craftsman operate on a square shaped split-rail system, while LiftMaster consists of one single solid piece of inverted t-shaped rail.