Shim a Door Lock with the "Credit Card Trick"

In Episode 10 of the Across The Peak Podcast, I mentioned that I always carry a store-loyalty card in my wallet. Used correctly this is an awesome tool for opening some locked doors. I mentioned that I’d explain how this technique works, so here goes!

Before we get into this, I have to throw out the disclaimer: never perform any lock bypass/defeat/picking techniques on any lock that you do not own or have explicit permission to access! Breaking into someone else’ home or business is a serious crime, and we do not condone such activity. We still think showing this material is important. First, there may be a time when you need to access a door in an emergency. Second, understanding how this technique works also helps you understand how to defeat it.

Why The Credit Card Trick Works

Before trying this technique, it is important to know why it works. Before we get into that, however, there are two facts you should know:

  • Fact 1: this technique will not get you through a door with a locked deadbolt. A piece of plastic applying force in a perpendicular direction will not disengage the deadbolt. This technique is useful only for doors secured ONLY with a locking knob. The moral of the story here is: if you don’t have a deadbolt on your home’s door, get one!

  • Fact 2: this technique will not always work. There is a very specific range of circumstances under which this technique will work, so don’t expect it to get you into everything.

 If the deadbolt is engaged…that’s a show-stopper.

If the deadbolt is engaged…that’s a show-stopper.

With that out of the way, let’s talk about why this works. The short “why” answer is that the door was either installed incorrectly, or is not correctly adjusted. The long answer is…well, longer.

Locking knobs rely on a spring-loaded bolt or latch to keep the door locked. You probably don’t think much about this bolt until you can’t get into your door, but it’s what’s doing the work. This bolt is rounded on one side, and flat on the other. The rounded surface is what allows you to slam the door; this is the part that strikes the door jamb when you close the door.

 A lock’s strike plate.

A lock’s strike plate.

The flat surface of the bolt is a little more complicated. Along this flat surface is another part that moves independently of the bolt. It is called the dead-latch. If you mess around with it you’ll learn a couple of things; if the dead-latch is depressed, the bolt can’t be pushed back into the door. If the dead-latch is extended, the bolt can be depressed, meaning the door can be opened.

 How your latch should function when your door is closed. The small portion should be depressed by the strike plate.

How your latch should function when your door is closed. The small portion should be depressed by the strike plate.

This is designed so that when your door is closed, the strike plate (the metal plate on your door jamb that interacts with the bolt) keeps this small portion of the bolt depressed. If all of this works correctly, your door is safe from the “credit card trick” because the bolt can’t be depressed.

So what makes the credit card trick work? The thing is, most strike plates don’t prevent that little latch from extending. Most doors are out of adjustment just a few months after being hung. Worse there is usually soft, pliable weather stripping around the door. If you can pull the door knob from the exterior and compress the weather stripping, there is a good chance you can get that dead-latch to fall into place.

How to Do the Credit Card Trick

You only need one piece of equipment to pull of this technique (assuming it works - remember, sometimes it doesn’t). That piece of equipment is a somewhat tough, yet flexible piece of plastic. I have found that gift cards - like the Starbucks card in the pictures- works well. Hereafter I will refer to whatever you use as the “shim.”

Before your begin shimming the latch, you need to ascertain that either:

  • There is no deadbolt present, or

  • The deadbolt is not locked. You can check to see if the deadbolt is engaged or not by using your shim. Simply insert it between the door and jamb, and see if it runs into the deadbolt.

 An extended deadbolt. Your plastic shim won’t defeat this.

An extended deadbolt. Your plastic shim won’t defeat this.

Once you are certain the deadbolt is not locked, you can begin. First, pull the door toward you as hard as you can. This gives the best possible chance that the dead-latch will extend fully. Insert your card between the door and the jamb, just above the knob’s latch. Insert it at an angle as shown in the photo below.

Credit Card Trick 2.png

Coming in at an angle like this helps the card to get between the strike plate and the bolt of the lock, by introducing it a little at a time. Keep applying downward and inward pressure on the card. At the same time, grasp the door knob and “wiggle” the rapidly in an inward/outward motion. It is possible for the bolt to bind against the strike plate; wiggling the door rapidly can take pressure of the bolt and allow the shim to slip in.

 This might not be quite enough of an angle. If you’re having trouble, adjust the angle at which the shim addresses the latch.

This might not be quite enough of an angle. If you’re having trouble, adjust the angle at which the shim addresses the latch.

Once the shim is inserted deeply enough it will separate the bolt from the strike face and the door will open. Voila! That’s the credit card trick. If the door doesn’t open after a few second, check your technique and try it again. If it still doesn’t open…it’s probably not going to.

We hope you never need this. If you do, we hope you know how to do it correctly.

Justin Carroll