Knock Box

This is cherry wood box I built for my nephew. The box locks from the inside using a servo and a groove in the wooden top. When turned on with a large switch ( my nephew wanted that specific “fighter jet” switch ) it will listen for a “shave and a haircut – two bits” knock. If the knock matches the servo turns and unlocks the box. The lock can be locked again by pressing a button OR by power cycling.


  • Dovetail joints
  • Hidden barrel hinges so there is no visible hardware on the outside
  • Uses an Arduino Pro Mini 5V
  • Knock is read with a Piezo Element. I broke 3 of these! The solder is very weak and the wire is very thin.
  • Lock is made using a Hitec Servo with a double arm that fits into a groove in the wooden top. Because the battery is contained in the box there is a slot that allows the box to be manually opened with a butter knife. The slot allows the arm of the servo to be moved and the slot tapers to finalize moving the servo arm to clear the top.
  • “Fighter Jet” switch to turn the Arduino on/off.
  • Two LEDs to monitor the activity. Red one to show the box is on/locked and blinks when a knock fails. Green one blinks to show the knock activity and solid when the box is unlocked.