Keyless door lock demands good sense of rhythm

The , which uses a tapped-out pattern on a $3 touch-sensor to open the lock.

Video demo after the cut

Rather than completely retrofit the door hardware, which landlords and college dorm authorities tend to frown upon, the system uses a high-torque servo to manually open the door knob inside.  This means it can be removed when you move-out, or shifted from door to door.  Maker Alex Leone experimented with using piezo sensors to track knocking, but the fact that the “key” would then be audible to those around discounted the idea.

Instead, a tiny touch-sensor passes on the signal to the Arduino processing board, which compares it to the stored version and lets you in if the match is good enough. 

“From personal experience (mostly my roommate has absolutely no rhythm), the pattern key could probably contain about 6 different lengths. Thus a key with length n will have 6^n possible combinations. To make the system more secure, there is no indication that an input is wrong; an attacker has no idea how long the key is” Alex Leone

Alex has put up the schematics if you’d like to try building your own.

via