Deadbolt locks provide added security, making them a common feature on most homes. This means that a broken key in the deadbolt can pose a major issue. If the door was locked, you may be unable to open it, while an open lock with a broken key doesn't provide any security. There's no reason to panic, though. Try one of the following methods to get the broken key out of the lock.
Method #1: The key is protruding
With luck, part of the key will remain protruding beyond the deadbolt, meaning that there is a small stub sticking out. You do need to proceed with caution, though, since this broken end may bend or break easily.
A pair of needle nose pliers and patience should solve the problem. If the door is unlocked, simply use the pliers to grab the protruding end of the key and pull it out of the lock. For a locked door, you will need to grasp the key firmly and gently turn it until the deadbolt slides out, then remove the broken key. Turning too quickly or forcefully could further damage the key.
Once this is done, call a locksmith so they can inspect the lock to make sure there is no further damage, and then make a replacement key.
Method #2: The key broke flush
More alarming is when the key has broken off flush to the lock, so there is no protruding piece to grasp with pliers. If the key broke off in an unlocked door, your best option is to call in a locksmith right away. They will be able to remove the key without causing any damage to the door.
For keys in locked doors, you may need to try a DIY method first so you can get into or out of the home. The most effective is to use a thin serrated blade. The blade from a jigsaw or a handheld mitering hacksaw works well. Remove the blade from the handle and then insert it into the lock until the blades hook on the serrated edge of the key. Then, gently pull back so that the blade draws the key out of the lock.
If the above method fails or only pushes the key in more, call a locksmith. Trying to further get the key out on your own at this point may only make the problem worse or it may damage the lock. The locksmith will have a key extractor tool or the knowledge to simply remove the lock and fix it.