How to Protect Your Lock From a Bump Key

Have a locksmith replace the pins in your spring-loaded pin lock with "mushroom pins." These have a narrower center and set falsely when the cylinder is turned if they aren't at the right height. These are more protective against lock picking than key bumping, though, since the latter will push the whole mushroom pin above the lock cylinder, making the narrow center irrelevant. If the labor cost is significant, you might want to consider giving up on directly protecting the existing lock and consider adding additional layers.

Use a layered approach. Install multiple locks and make sure they are of different brands and types. This requires the burglar to have more than one bump key. An apartment building in which everyone has the same kind of lock can be fully unlocked with a single bump key.

Install a pick-proof lock, either in addition to or as a replacement for your spring-loaded pin lock. If a lock is pick-proof, then it is bump-proof, since the two methods rely on the same cylinder-spring structure. Another option is to install keyless locks such electronic, magnetic, combination or rotating-disk locks. You can purchase pin locks that are bump-proof without being pick-proof, such as locks that can be made with built-in trap pins. These are pins that don't engage if the pin isn't fully supported by the key. Bumpstop locks have trap pins that prevent the transfer of force between paired pins.

Shallow drilling is another option. These are pins in which one of the pin-spring-pin stacks is shorter than the others. So a bump will have more trouble lining up all the pins.

Buy an alarm. Multiple layers are more effective when they are varied.

Display visible deterrents. The more protections the burglar sees, the less likely he will attempt your lock in the first place. Such deterrents include alarm signs and stickers, bright lighting, lights left on inside and the barking of a family dog.