Open your garage door with a secret knock: “Open Sesame!”

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The Issue:

Typically, opening a garage door requires either a key, remote control, or phone app. 

But wouldn’t it be convenient to be able to open your garage door just by knocking on it in a special pattern (Figure 1)?

Fig. 1: With some additional hardware, it’s possible to set up a garage door to open just by knocking on it!

As it turns out, it is NOT convenient at all!

(But read on anyway for a rare example of an “actually implemented in reality” Worst Plan.)

Proposal:

Figure 2 shows the basics of the system: it’s just a microphone that detects the sound of knocking and can press the garage door opener button if it detects the correct “secret knock.”

Fig. 2: Conceptually simple!


In order to make this a reality, we just need a a tiny computer that can activate the garage door remote control.

Physical materials used:

  • A USB microphone
  • Raspberry Pi computer
  • A sacrificial garage door remote
  • Some wires to connect the Pi to the garage door remote
  • I guess you also need a garage door, I hadn’t really considered that

Software used:

The software continually checks the microphone for the purpose of detecting a knock (Figure 3).

Fig. 3: Here’s what the terminal output looks like from the program that listens for the audio: it’s just listening for “volume > cutoff” to detect a knock. In this case, it detected the secret knock rhythm (2 knocks, pause, 3 knocks) and would have opened the garage door, except that we were in a “dry run” test mode.

The most complicated part of this system turned out to be actually connecting the remote to the Raspberry Pi.

Fig. 4: The process of figuring out how to actually activate the garage remote using the Raspberry Pi’s GPIO pins (which can send an electrical signal—in this case: “open the door”—to a connected thing).

Fig. 5: The final setup, with the Raspberry Pi and garage door remote in a hopefully-bug-proof plastic container (right). The USB microphone (not shown) is connected by a long USB cord and trails off to the garage door, where it’s been hung on a small hook.

Bonus security feature (Bluetooth):

To reduce the chance of accidental and/or malicious garage-door openings, the program also has the ability to only open the garage door if a recognized Bluetooth device (e.g., your phone) is nearby. With this enabled, eavesdroppers won’t be able to open the garage door even if they use the correct knock.

PROS: This actually works in reality!

CONS: Knocking on the outside of a building with your knuckles is surprisingly painful, and it turns out to be way easier to just use a phone app to open the door. But the principle is sound!

Originally published 2026-03-16.


Special thanks to M.M. for bringing the required electrical engineering expertise to Figure 4.