Understanding Combination Padlocks

The original keyless entry device offers convenience but also has vulnerabilities

The basic design for the modern combination padlock has been around since 1878, and the basic strategies for cracking these locks are probably just as old. Combination padlocks can be useful for low-security applications like securing a gate, a shed door, a locker, or a small lockbox, where you simply want to add an extra level of deterrence against opportunistic thieves inside an area that is already protected from unauthorized access. Combination padlocks should not be used to secure high-value items or in areas that are prone to crime because many types of padlocks are so vulnerable to picking or cracking.

Types of Combination Padlocks

There are two main locking mechanisms for combination padlocks.

The first is the dial lock, which consists of a dial spindle attached to 3 wheels and a drive cam. Each wheel has a notch in it corresponding with a number on the dial. When the notches line up, the lock will open.

The second type of combination padlock is known as a multiple-dial lock and consists of several independently rotating discs moving around a central pin. When the notches in the discs line up with the teeth on the pin, the lock will open.

Either type of lock may be available in reprogrammable styles, allowing the owner to input a different combination when the lock is in the open position. Some reprogrammable combination locks require a special tool; if you lose this tool you will not be able to reprogram the lock without the help of a locksmith.

Combination Padlock Vulnerabilities

Any type of combination padlock can be opened by a determined thief, either by cutting, smashing, picking, or cracking the lock. Fortunately, if you understand these vulnerabilities, you can take steps to address them.

For example, buying a shrouded padlock with a strong body can help prevent brute force attacks as well as cutting and picking. A shrouded padlock is designed to cover most of the shackle, preventing someone from removing the lock with boltcutters. Plus, because the shroud covers the point where the shackle enters the lock body, it prevents someone from using a shim to pop the lock open.

This leaves vulnerabilities associated with cracking the lock, or opening it by figuring out the combination. If you pick a weak combination for your lock, such as your address or your birthday, a thief may be able to guess it and open the lock that way. Also, some thieves have the skill to open the lock by listening or feeling for the points where the discs catch. You can help protect against this possibility only using combination padlocks inside areas or buildings that are already secure, and by placing them in highly visible and well-lit areas where a person tampering with them would be noticeable.