HOWTO force a padlock with a tin-can shim

This short video illustrates a simple procedure for forcing open standard padlocks with a shim snipped out of a tin can. The technique is old, but this is a good, lucid explanation of it. Kids have been doing this for years, but schools and gyms still recommend these broken locks -- and the manufacturers keep making them, which is practically criminal negligence. Link (Thanks, Kevin!)

See also: HOWTO pop a combination lock with a beer can


  1. “this is a good, lucid explanation of it”

    If, that is, you can understand the words the narrator is saying! I guess the mouth-full-of-marbles delivery has a certain charm, however–he’s keepin’ it real as a teen geek.

  2. This isn’t anything new, as the article points out. It’s also worth mentioning that the FUD of “criminal negligence” is a bit absurdist. Anyone with 15 minutes and 5 dollars can learn to pick 95% of locks out there. After all, locks only keep honest people out.

    Another fun one : Take a Bic pen, and cut it in half. Insert into the C-clamp circular locks that college kids use on their bikes. The tumblers will eat teeth into the plastic, and you can then turn it to unlock the bike. Me and my mates did this all the time at uni.

  3. I agree with TheRascalKing – any lock can be broken by those with the right knowledge. (It’s similar in many ways to the fact that any DRM can be broken) Of course if you have something really valuable, it’s worth investing in the latest, harder to break (but not unbreakable) locking technology, but for most purposes you can rely on the fact that most people don’t know how to do it, and that most people don’t want to steal your stuff (or don’t want to go to any effort to do it).

  4. The hack for cylinder locks is an interesting example of negligence — the locksmithing people have long practiced security through obscurity, and thus it is that locks with known defects (susceptibility to bumping, cylinder locks that can be opened with Bic pens) stayed in production for years (decades!) even though they were known to have trivially exploitable flaws.

    Indeed, it was the infosec people who exposed both of these long-running flaws — the ethic of full disclosure has been slow coming to physical security.

  5. We shouldn’t expect locks to be absolutely invulnerable, which I think you might be implying. What we should expect is that locks and other security measures withstand an attack long enough for someone to notice the attack and do something about it.

    The problem with these cheap locks is that their ability to withstand attacks is much less than advertised. It may not matter in, say, a high traffic area, but at least the consumer should be aware of how long these locks are expected to stand up to a determined attack.

  6. Sure, of course they needn’t be impregnable — but when a lock mechanism is known to be vulnerable, in seconds, to unskilled attackers with no special apparatus (tin cans and Bic pens don’t count), then you’re basically selling fancy hook-and-eye latches and pretending that they’re locks.

  7. And of course, in the case of things like Kensington laptop locks and Kryptonite bike locks, they were advertised as nigh-impregnable, when they were really barely more than papier mache.

  8. Masterlock sells one that has a laser cut key and precise tumblers making it more difficult to pick. It also has a thick metal guard on the sides to prevent shims and make it very difficult to cut. I bought mine for about $15. It’s by no means absolute security, but it’s better than most padlocks.

  9. This works with both keyed and combination padlocks, though this video makes it look easier to do than in real life. Basically what you are doing with the shim is forcing the triangular locking latch away from the U-bar.

    I’d imagine he used a cheap combination lock that had a lot of space between the U-bar and the padlock holes in which to insert the shim.

    * Some padlocks use a latch on both sides as a prevention measure, requiring two shims, which is much more difficult given the confined spaces.

    * Completely round “security” padlocks combat shims by forcing it to bend into a poor position and crumple (I use one of these).

    * A bunch of “Master” brand locks use a straight piece of wire instead of a triangular latch, which is pretty much invulnerable to conventional shim-based attacks. They’re also pretty damn hard to break open.

  10. can of compressed air, upside down, cool the exposed metal, whack soundly with hammer, no more cheap lock

    I actually found a fabulous video at Instructables!/?comments=all

    the point is not that it is a better method, just that there are many ways to quickly and cheaply get a lock off.

    Heck, bolt cutters are small enough to hide under a coat, and you can rifle your ex’s locker with no issues.

    good source for lockpick tool and instructions:

    RacsalKing is right, locks are a deterrent. Only

    Nerkles asks: What is a good lock? Well, there aren’t really many out there. The best lock? Carry important stuff with you.

    The Union DTEC is almost decent, but? in the end, if someone wants your stuff, they will get past a padlock

    hook up an Auto Taser?


  11. So I tried this with the blue-dial combination Master Lock padlock I used to keep my organic chemistry glassware locked away when I was an undergraduate chemist, and I can’t make it work. I have made no fewer than 5 shims, following the video as closely as possible, and it simply does not work. The stem when the shim is pushed down into the lock inevitably fails; the shim will fit into the lock casing but sticks, and as force is increased, begins to wrinkle and bend. Perhaps some lubricant on the shim would help, but the fact of the matter is that this is no where near as easy as the video’s narrator (who has had the luxury of choosing and practicing with his own demonstration lock) makes it seem. Anybody else actually try it?

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