So the first time most people see a padlock pop open with a strip cut from a soda can, they don't believe it. No key. No picking. No drilling. Somebody slides a little curl of aluminum down the side of the shackle, gives it a twist, and the lock just falls open. And then they want to know how, because a second ago that padlock felt like security.

That little curl of aluminum is a shim. And it's one of the oldest, simplest bypass tricks there is. So let's talk about how it works, which locks it walks right through, and which ones it can't touch. Because the honest answer to "should I be worried about this" is that it depends entirely on the padlock.

What a shim actually does

Here's the thing a lot of people get wrong. A shim isn't picking the lock. It never touches the pins or the keyway at all. It goes after a different part of the lock, the latch that holds the shackle down.

On a lot of cheaper padlocks, the shackle (the U-shaped metal loop) is held closed by a spring-loaded latch that snaps into a notch cut into the shackle. Turn the key, the latch pulls back, the shackle pops up. A shim skips the key entirely. You wrap that thin piece of metal around the shackle, slide it down into the tiny gap between the shackle and the lock body, and work it into the spot where the latch grabs. The shim wedges between the latch and the notch, pushes the latch back, and the shackle is free. Done.

And here's a detail that surprises people: cheap combination padlocks work the exact same way. There's a latch behind that dial, the combo just pulls it back, so a shim walks right past your secret code like it isn't even there.

One more bit of trivia. You already know this move from the movies. Every time a character slips a credit card into a door frame and pops the latch open, that's the same principle, something thin and stiff pushing a spring latch out of its notch. Old-school lock folks call that move loiding, named for the celluloid strips people used before credit cards existed. And it's real enough that we make door shims and an actual credit card latch slipper for exactly this. A soda can shim is the same idea, just curled around a shackle instead of slid into a door frame.

The soda can version is just a shim you cut yourself. An aluminum can is thin, springy, and free, which makes it the classic material for showing the trick. But purpose-made shims do the same job faster, and they don't crumple halfway through the way a homemade one can.

Which locks it opens (and which it doesn't)

Now, this is the part that actually matters for you, so pay attention here. Shimming is not a universal skeleton key. It beats a specific kind of lock, and better locks are built to stop it.

  • Easy targets: cheap luggage locks, gym and school locker padlocks, and low-end hardware-store padlocks that use a single spring latch on one side of the shackle. These are the ones that shim in seconds.
  • Harder or shim-proof: better padlocks use a dual ball-bearing locking mechanism instead of a flat latch. Two hardened balls seat into the shackle from both sides, and there's nothing flat for a shim to wedge past. Disc detainer padlocks and most high-security locks don't have a shimmable latch at all.
  • Mostly doesn't apply: deadbolts and door locks. The soda can trick targets the shackle latch, and your front door isn't held shut by a shackle. There is a cousin of this move, a thin lab-style shim that can slip certain deadbolt and key-in-knob cylinders by working the pins instead of a latch, but that's a different tool and a different skill.

So if the padlock guarding something you care about is a five-dollar hardware-store special, it's probably shimmable. If it's a decent padlock with ball bearings, it isn't.

Why we teach this instead of hiding it

Some people get uneasy about explaining a trick this simple. I get it. But here's how I see it, and it's the same way I see all things vulnerability related. The shim trick has been around for decades. The people using cheap padlocks to guard things aren't made safer by not knowing their lock is weak. They're made safer by finding out, and then spending ten or fifteen more bucks on a padlock that isn't.

Knowing your gym locker padlock shims open in five seconds isn't scary. It's useful. It tells you exactly what that lock is worth: it keeps honest people honest, and that's about it. Which is fine, as long as you know that's the job it's doing.

And since it always comes up: are shims even legal? Owning them is legal in most of the US, same as lock picks, but a few states have their own rules, so check yours before you order anything. Honestly, the way you use them is the simple part. Your locks, or locks somebody actually asked you to open. Stick to that and you're fine.

Okay, so how do you actually do it?

Here's the whole process for opening a padlock without a key, start to finish. Fair warning before you start: can aluminum is super thin and the cut edges are sharp, so go slow and mind your fingers.

  1. Cut a flat rectangle out of any standard aluminum can, bigger than the shim you need.
  2. Cut the shim shape out of that. If you printed the template, trace it. If you're freehanding, you want a strip with a rounded tongue in the middle that can slide down along the shackle.
  3. Fold it. The folds stiffen the aluminum, give you tabs to hold onto, and curl the tongue so it wraps the shackle instead of lying flat against it.
  4. Wrap the shim around one leg of the shackle and slide it down into the gap between the shackle and the lock body.
  5. Work it down into where the latch grabs, then pull up on the shackle. The moment the shim slips between the latch and the notch, the shackle pops.

If nothing gives, don't muscle it. Try the other leg of the shackle, since some locks grab on the side you didn't expect, and a few grab both, which is why purpose-made shims come in sets. No big deal, pull it out and go again.

Try it, and upgrade what needs it

Now, this is one of those things that makes way more sense the second you try it yourself. Grab a cheap padlock you own and give it a shot. If you're going the soda can route, we made that part easier too. The Beverage Breacher, which is what happens when you let lock people name things, is a free 3D-printable template you trace and cut around, so your can shim comes out the right shape on the first try instead of the fifth. It's even keychain-sized. Or skip the crafting and use a proper set of padlock shims to feel how the latch gives way. There's no substitute for watching a lock you thought was solid drop open in your hand. It's the fastest way to learn what your own locks are actually made of.

Shimming is one of a whole family of bypass moves that skip the keyway entirely and go after the mechanism instead. If that's the part you find interesting, our bypass tools collection is all of them in one place. And if you'd rather learn the craft of actually picking a lock, that's a different skill worth building.

Anyways, go look at what's actually hanging on your shed, your locker, your gym bag. I'd bet at least one of them is a five-dollar spring-latch special. Swap it for something with ball bearings, and keep the old one, because a padlock you can already beat is about the best practice lock you can ask for. And as always, I appreciate you.