Today I’m going to take you through how to pick a combination lock. A couple of weeks ago we picked up a pair of 4 digit combination padlocks from Bunnings to see if we could easily bypass them. As it came in a pair we thought we could have one for picking and one to cut open so we could see how it all works inside. Understanding how it works lets you work out if there are multiple ways to bypass the lock when you don’t know the code. So in this article, I will take you through cutting the lock open, show you how it works, and then how we bypass it. We only found one bypass for this lock but its a really easy one and you can pick it easily in under a minute. This is a common problem in these types of combination locks and is the same method we used to bypass this Abus combination padlock.
If you don’t want to read this whole article, jump to the end and we have a video on our YouTube channel which takes you through everything we talk about in this article and also a demo of how to pick the combination lock.
Pulling Apart a Combination Lock
First, we took a look at the lock to see if we could work out how to pull it apart. It had a plastic covering that was easy to pop off with a flat head screwdriver. You can see this plastic piece wrapping around the top and sides of the locks.
On the outside of the case were four round markings. We figured these were probably rivets as you wouldn’t want to use screws or someone could just unscrew the lock to bypass the lock. The only way to get rid of the rivets is to drill them out. So we went to the garage, put the lock in the vice and drilled out the rivets. We then used a screwdriver and poppped the case open, VERY gently, so all the bits inside didnt go everywhere.
Inside a 4 Dial Combination Lock
Inside the case, there were three main bits, along with a spring and washer.
The shackle is the piece of metal you see sticking out of the padlock which you lock around things. Setting the right combination releases the shackle and the lock can open.
There were 4 gears, one for each dial. These wrap around the shackle and sit inside the number dials. They are the bit that stops the shackle moving and the lock opening. When the gears are all aligned (using the dials), the shackle is released and the lock opens.
The dials are the round bits you see on the outside with the numbers on them. These are the bits you rotate to enter your lock code so the lock can open. These dials fit over the gears and when you turn the dial it turns the gear underneath.
How Does the Combination Lock Work?
Here is a close up of the shackle with the gears and dials removed. It has 5 pins on the side. One stops the shackle sliding out of the lock, ad the other 4 are for the gears… one for each gear. These are part of the shackle and stick out stopping the shackle sliding through the gears. If the gears are aligned, these pins can slide through the gears allowing the lock to open.
Here is the gear by itself. You can see a groove on the inside of the gear on the right, like a little gate. This is the bit that lets the pins on the shackle move through the gear. If the shackle pin isn’t aligned with this groove it won’t open. If the gears are aligned, the shackle pins slide through this gate and the lock opens.
In this picture you can also see a groove at the top. I’ll get to this groove in a minute cause its actually the most important bit for picking this lock.
In this photo, we have put part of the lock back together so you can see how it all fits together. We have the shackle, one gear and one dial.
The pins on the shackle are on the right of the picture where you cant see them. You can sort of see part of one if you look closely.
The gear has been rotated so that little gate we showed is on the right so it lines up with the shackle pins. If we pulled on the shackle it would slide through the gear. So this is the open position for this gear.
Note that the dial is on number 3. So this dial’s correct combination is 3.
And see that groove I said was important? It’s pointing straight up when the dial is in the open position. If we had all 4 dials installed and all in their open position, we would have 4 of these little grooves pointing upwards. This is how we decode this lock.
How to Pick the Combination Lock
All you need is a decoding tool, a shim or something else really thin. In the video, we use a feeler gauge. If you slide it down next to each dial you can feel for this groove. When the lock is in the open position, the groove will be at the top and you can feel it with your tool. If you cant feel it, rotate the dial and keep feeling. Once you can feel it, move on to the next dial. When you have all 4 notches at the top, you have the right combination and open!
The interesting thing is we have no idea why this groove is there. It doesn’t seem to have any purposed but makes it easy to pick the lock. Very weird. If you know why it’s there let us know!
And that’s all there is to it. Here is a video below that goes through all the above and has a demonstration of me feeling for the grooves and opening the lock. Check out our combination lock bypass playlist on our YouTube channel as well as there is another video where we bypass the Abus lock using the same technique. We haven’t cut that lock open but by the feel of it, it has a groove as well.
We would love to hear from you in the comments so let us know if you have any techniques you recommend or any comments about this article, the video or locks in general. Until then, have fun lock picking and we will be back soon with another lock bypass!
Boo has a passion for bypassing tamper evident devices, having first got her tiny 6 year old hands on them at BSides Canberra in 2017. When she isn't bypassing tamper evident devices or lock picking, she can be found writing code, programming her robot, performing gymnastics manoeuvres or taking other children down in the MMA dojo.