Rolling Code

Rolling code—also marketed under brand names such as Security+ (Chamberlain/LiftMaster), Intellicode (Genie), and Whisper Drive (Sears/Craftsman)—is an encryption-based protocol used between garage door remotes and openers. Both the remote and the opener's receiver share a secret cryptographic seed. Each time the remote's button is pressed, both devices advance their internal counter and generate the same new code using that counter and the shared seed. The opener accepts the transmission only if it matches the expected next code (or a small lookahead window to account for button presses made out of range).

Rolling code replaced the older fixed-code DIP switch system after researchers demonstrated that fixed codes could be intercepted and replayed with inexpensive radio equipment—a technique called a replay attack or code-grabbing. Because a rolling code is valid for exactly one use, an intercepted transmission cannot be replayed to gain entry.

When you press a remote out of the opener's range, the remote still advances its counter but the opener does not receive the signal. If this happens many times in a row, the remote and opener can fall out of sync. Most openers tolerate a window of a few hundred missed transmissions before they stop accepting the remote. To resync, the user presses the learn button and re-pairs the remote.

All modern residential garage door openers sold in North America use some form of rolling code. If an older opener uses fixed-code DIP switches, the security benefit of upgrading to a rolling-code opener is significant and the process is straightforward.