When choosing an iron padlock, it is important to consider whether it is susceptible to impact. Even if the lock is made of strong and durable material, it can be opened by collision. Using a special crash key-also known as a knock key-a motivated thief can pry open a traditional marble lock.

What is lock collision?
Not to be confused with picking, collision involves using the collision key to access and open the flip lock without the original key. A special collision key is used to mimic the mechanism of the original key. The thief inserts a part of the hitting key into the lock, at which time he or she will try to open the lock by "hitting" the key inward.

To better understand how collision works, look at the traditional pinball lock. In a pin lock, there are multiple spring pins. Each spring pin consists of two parts: the key pin and the drive pin. When you insert the original key into the lock, the key pin and drive pin of each pin will be perfectly aligned, thus opening the lock.

The impact key has teeth that can knock the key pin into the pair of drive pins. After successfully aligning a stitch, the thief will move to the next stitch. Only after all the pins are aligned, the long shackle padlock will open.