On Thursday, well-known hacker Samy Kamkar published on his website the blueprint and software code for a 3-D-printable Arduino-based lock-opening robot he calls the “Combo Breaker.” Attach it to any of millions of Master Lock combination locks, turn it on, and it can take advantage of a Master Lock security vulnerability Kamkar recently discovered to open the lock in a maximum of five minutes with no human interaction. “The machine pretty much brute-forces the lock for you,” says Kamkar. “You attach it, leave it, and it does its thing.”

Kamkar’s robot consists of little more than a stepper motor, an Arduino chip that runs his cracking algorithm, a lever to pull the shackle, a rotor with a 3-D printed attachment to the lock’s face, and an optical sensor that tracks the location of the lock’s dial as it turns. All together, he says he built his prototype for less than $100. Here’s Kamkar’s video breakdown of the robot’s creation.

Master Lock didn’t immediately respond to Wired’s request for comment. But Kamkar says his cracking technique is likely no major surprise to the lock maker, nor should it necessarily register as a serious security crisis. Master Lock gives its locks a 1-to-10 security rating displayed on its packaging, and the locks he tested were all rated 3. “The moral is pretty simple,” he says. “If you’re trying to protect valuables in a storage locker, you should probably be using a better lock.”

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