How to Bump a Lock
“Bumping” is a lock-picking technique that refers to the repeated striking motion used to dislodge the pins inside a lock. Doing this requires a specially cut key, known as a bump key, that with the right application can be used to force open 90% of cylindrical locks. Despite its ease, lock bumping should only be performed in emergency situations, like when you’ve locked yourself out of your own home, and should never be used for trespassing or other illegal activities. To successfully bump a lock, all you’ll need is a bump key, a blunt object and a little patience.
Part One of Three:
Making a Bump Key Edit
Start with an ordinary key. Find a key that fits into the lock you’re attempting to bump. The teeth of the key won’t be the right size or dimension to move the pins, so the key won’t turn, but it’s important that it be able to slide inside. Locks and keys come in all different makes, but many keys will fit into a standard cylindrical home lock. 
- If you’re fashioning your own bump key, pick a key that you don’t use regularly. Try it out in a few cylinder locks to see if it fits before filing it to the right specifications.
- Lock bumping is such a potential problem because it can be performed with almost any key. 
Identify the position of the valleys in the teeth. Look at the key and observe the spacing of the teeth. At the bottom of each tooth is a flat area known as the “valley” that separates the teeth. In order to be able to disengage the pins of the lock, these valleys will need to be filed down all the way to the main shaft of the key.
- When it comes time to modify the key, be careful not to file the valleys too shallow or deep. If the spaces between the teeth are not at the right depth, the key will be useless.
File the valleys down to their lowest position. Use a manual file (a wedge or triangular shape will work best) to shave down the valleys between each tooth on the key. The key should have a jagged, zig-zag appearance when you’re finished. Once the valleys are as deep as they can be, the teeth will be long enough to push up the pins in the lock when the key is struck a certain way. 
- Locksmiths refer to keys that have been ground down to a serrated pattern with sharp, even peaks and valleys as “999 keys.” 
- Pre-cut bump keys can also be bought from unscrupulous vendors, but be warned: possession of a bump key is generally regarded as a cause for criminal suspicion by law enforcement.
Make sure the teeth are level. File each valley down to the same point along the shaft of the key. If the valleys at the front of the key are deeper than those in the back, the key won’t be able to slide into the lock. If the valleys in the back are deeper, you may have difficulty pulling the key out of the lock after bumping it. There should be a very small triangular depression in the shaft of the key at the bottom of each valley. 
- Locksmiths and services that grind key duplicates are capable of precisely cutting 999 keys, but you might get some strange looks if you ask for this to be done.
Insert the key into the lock. Fit the key into the lock. Push it in until it stops, then pull back slightly until you hear or feel the last pin click. This puts the pins in the right position to be manipulated by the teeth of the modified key.
- Keys of roughly the same size will often fit any lock with the same mechanism (like a cylindrical lock). 
- Insert the key slowly and carefully to make sure it doesn’t get stuck. The deeper valleys might make it prone to getting caught on the pins.
Begin turning the key. Try turning the key in the unlock direction (usually counterclockwise). Keep constant pressure on the key as you work. It won’t move very far initially, but if you’re able to jostle the pins just right with a well-placed strike, the key will effortlessly turn the rest of the way. Grip the key near the teeth to allow yourself room to hit the back end of it. 
- Don’t turn the key too hard. It will be weaker since you removed metal from the body, and twisting it forcefully while striking it might cause it to break off in the lock.
Strike the back of the key with a blunt object. Using a mallet, the handle of a screwdriver or another broad, blunt object, strike the rear edge of the key as you continue trying to turn it in the lock. This is what is known as the “bump.” You’ll need to hit the key quite hard, as the technique requires that that force be transferred through the lock. If you’re successful, the pins inside the lock will jump momentarily, creating enough space for the key to turn the rest of the way. 
- Hit the key directly on the end, not at an angle.
- The bump won’t work if the key is inserted all the way into the lock. Pull back on the key until you hear the first click before attempting the strike.
Repeat until the key turns in the lock. If you’re unsuccessful on your first attempt, try wiggling the key and hitting it again. Repeat this process, turning the key in the unlock direction the entire time, until the pins catch. If after multiple attempts the key still won’t budge, remove it from the lock and try inserting it again, pulling back just a little to put it in the right position to dislodge the pins. 
- If you’ve tried over and over and still can’t get the key to turn, either the grooves you filed in the valleys are not the right length or the deadbolt needs to be turned in the opposite direction.