Biometric Door Lock

This one started as a low-grade arms race with my fraternity brothers. They had a habit of getting into my room and messing with my stuff, and the house’s master key made it easy at first. I bought a new doorknob that didn’t match the master key, so they picked the lock. I made that harder, so they tracked down the exact same doorknob model I’d bought, figured it used the same key, and let themselves back in. At that point I decided the only real fix was removing the key from the equation entirely.

I took apart my doorknob to see how it actually worked. The mechanism turned out to be simple: a square metal shaft rotates when you twist the knob, which pulls a latch in and out of the door frame. Once I understood that, I cut off the shaft, sourced a servo motor, and designed and 3D-printed a custom adapter to connect the servo directly to the latch mechanism. I programmed an Arduino Nano to read a fingerprint sensor and drive the servo, so a verified fingerprint, mine and only mine, is what rotates the latch instead of a hand turning a knob. I also designed and 3D-printed a housing to conceal all the electronics and wiring, leaving just the fingerprint scanner visible on the front.

It’s not a high-security lock by any real standard, and that was never really the point. What mattered to me was the process: taking apart an everyday mechanism, understanding exactly how it worked, and rebuilding it to do something new. It was also just a genuinely fun way to end an escalating prank war on my own terms.