On the Vulnerabilities of Combination Locks


Back in December, just a few days after Kelly came home from the hospital, I went to the gym for a badly needed workout. I put my wallet and car keys in a small set of lockers located on the weight room floor. Those lockers (pictured above) have a built-in combo lock where you can set the combo yourself. Unfortunately something went wrong. When I went back to retrieve my belongings the combo I had set did not work. I asked a staff member to find the master key to open the locker. He informed me that the boss had it and that he wouldn’t be back until after the holidays. I panicked. How would I get by without my keys, credit card and driver’s license? Then I remembered an idle afternoon back in the summer when I attempted to learn how to crack combo locks.

The efforts of that afternoon paid off. After around five minutes of practice on the other lockers I figured out how to open the lock and I manged to retrieve my belongings.

Combo locks all work the same way. The internal mechanism has three or four wheels that must align to open the lock. More expensive combo locks have false gates to make them harder to crack. The cheap built-in locks at the gym had no false gates. Opening the lock was as easy as turning the numbers until I felt a subtle resistance. The process reminded me of playing a musical instrument. All it takes is a little finger dexterity and practice.

Should you find yourself in a similar situation, you’ve got a couple of options for opening a combo lock:

  • With a shim:

  • With some math:

Both the shim and the “math” methods take practice. I have not been able to open the lock I’ve been practicing on with either of these techniques. Of course, the easiest method is just to pry open a locker with a screwdriver or crowbar. And many locks can also be defeated by drilling them.

Lastly, let’s say you have an open combo lock but have forgotten the combo. You can figure it out by peering into the opening:

In addition to adding a James Bond villain skill to your mental toolkit, consider this post as a warning. Don’t leave valuables in a gym locker. I could have easily opened the other lockers, pulled out wallets, copied down credit card numbers and put the wallets back. My fellow gym goers would not have known anything was wrong until their credit card bills arrived.

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  1. Huzzah! Today I learned something useful. Thank you. (and hugs to Kelly – hope she’s healing just fine)

  2. That was the worst possible time for your keys and wallet to be inaccessible. It’s great that you had the skill to open the locker.

    Your story reminded me of a time when I bought a large kitchen cabinet at an antique store. I was told that the cabinet was from Denmark. Maybe it is–I don’t know. It’s obviously old. I’m guessing that it was made in the early years of the 20th century. The cabinet has three compartments with doors–and glass in the doors. The man who sold me the cabinet handed me an old skeleton key and said that it was supposed to open the top compartment–but that the lock didn’t work–and the compartment wouldn’t open. I mentioned my problem to my father, and he said not to worry–he would open it for me. He spent about an hour, very carefully turning the key and jiggling the lock. All of a sudden, he had the compartment open.

    Even though this wasn’t a padlock, I think that he must have used a variation on your technique to open the old lock with the skeleton key.

    • To be honest I don’t know much about induction stoves. In general, I’m more a fan of gas if it’s available.

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