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RFID card readers becoming passé? Maybe what you need to guard the door to your high-tech lair is a secret knock detecting door lock. Using an Arduino and a bunch of parts found around the lab, Steve Hoefer built a device that unlocks your door when it receives a certain knock pattern. It works by counting the time between successive knocks, and can be re-programmed at the touch of a button.

Of course, this system is susceptible to a replay attack, because anyone can listen to the knock pattern and then know how to get in. If you are planning to use something like this, I would recommend either incorporating a timestamp into the message, or using a series of one time knocks, in order to make it harder to break into. Actually, that might make it more secure than a regular lock.

  • Sam Owles

    The website appears to be down, is there somewhere else we can see the detailed plans?

    • Steve Hoefer

      Unfortunately getting linked on Gizmodo and a few other high traffic sites has overloaded my server for the day (Nov 3) and my web host is not being service-minded today.

      I’ll be moving to a new host soon, but in the meantime it should be back up after 12:00 (midnight) CST. Hopefully it should stay up.

      Sorry for the trouble. Trust me when I say I’d rather no one had to deal with the outage.

  • César Abarca Landete

    Yes, is very useful, but I think is better together with extra system.Thanks for you idea.

  • César Abarca Landete


  • Davy Braun

    One alternative against replay attack could be having 2 or more alternative knock, and each time you do knock 1, next opener knock would become knock 2, etc…

    That way, if an intruder passes right behind you while being unaware of the alternate knocks, she’d be left dumbfounded.

  • Andrew Gamal

    I want to make face detection with knock detection with arduino can u help me?!