How to tell if your locks have been tampered with

Burglars may try a number of methods to try and gain access to your home, including picking your lock. The most obvious signs your lock has been tampered with are visible dents and scuff marks around the keyhole. While these are quick and easy to notice, here are specific signs of lock tampering that you can look for and measures you can take to help prevent unauthorised entry.

When you suspect lock tampering—or worse, a break in—the first thing to do is remain calm and assess the situation. What evidence do you have? For example, is anything inexplicably missing, moved, or broken? Any window, lock, or door frame deformed, smashed, or broken? If you have evidence like this, call the police to report it. If not, you might look a little closer for indications of tampering.

Before you go looking for signs of entry, however, it might help to have a basic understanding of the three main ways burglars go about getting through locks.

This is the hastiest, and therefore messiest, form of attempted break-in. Often a criminal will try to bash in a lock, drill through a deadbolt, or kick down a door, leaving a trail of twisted metal and splintered wood. There are less obvious ways to force through a lock though, so you might also look for some of the following signs of unnatural wear.

• Paint circles from lock fixture movement (like it was loosened and retightened out of place)
• Bent deadbolts or latches
• Warped doors/doorframes

If you notice that your key is suddenly harder to turn than usual, this could indicate pin deformation—a result of more refined methods of lock manipulation like bumping or picking.

Since the early 1900s, locksmiths have used a secretive technique called "bumping" to open locks in a hurry. In 2005, a Dutch talk show revealed the process and, since then, the technique has been picked up by countless burglars worldwide.

To do this, burglars file down the teeth of a key into several points, sort of like a little saw. Next, they insert this “bump key” all the way into a compatible keyhole and withdraw it with one click. Then they strike it abruptly with a blunt object, withdraw one click again, and repeat until the lock tumblers have all caught. Finally, they turn the key and open the door.

When done correctly, this method leaves little trace. Sometimes, however, hasty amateurs can leave identifiable marks.

• Fresh nicks around the edges of the keyhole from pounding the key a little too forcefully
• Shiny metal edges that look like they’ve been recently hit

The third and most traditional method of tampering with locks is "picking." This is where a person uses small tools like a flat screwdriver to turn the lock and a pick (sometimes even a dental pick) to rake the pin tumblers. Like bumping, once the tumblers catch the lock easily turns.

This takes more time and expertise than bumping, but is gentler and therefore unlikely to leave indications like warped pins or bolts. Nevertheless, as picks and shims (i.e., screwdrivers) wiggle around inside, they can cut into the edges, leaving marks.

• Tiny scratch marks, showing fresh, shiny metal around the key hole (finer than from a key)