Some things you just can’t prepare for. You drop your air conditioner while taking it out of the garage and crack a tile or damage hardwood floor; there’s no real way to expect that, other than asking the brawny neighbor to help you out. A rock hits your windshield on the way to work and you get a crack; what could you have possibly done to deter that? As Elvis Costello (and yeah, okay, a lot of more people before him) said, accidents will happen.
Having your key break-off in a lock is about as common as having your windshield cracked by some rebel pebble flicked off the pavement, and it is, by every measure, something that can be handled without professional care. You’ll need WD-40, or a similar spray lubricant; even spray olive oil could work in this situation. Besides that, you will need utensils for removing the key, chiefly any sort of thin saw blade and something to pick the protruding key piece out of the lock. Tweezers or pliers are your best bet and are easy to find around the house usually.
Begin by spraying the lock with the spray lubricant, to give you some help when it comes to dislodging the key piece from the lock. Thin saw blades are best for this situation, as the blades can easily hook into the grooves of the key. On one side of any key (take a look at one right now), the indent of the grove is more uneven, less smooth, and has a greater indentation. That’s the side you’re going to want to insert the saw blade into the lock. Once its in as far as possible, twist it a bit and try dragging out the key with the saw blade; you really only need a little bit but get as much as possible.
Once you get a little bit out, you should be able to grab the lodged key piece with the tweezers or pliers and presto! Now, in some cases, the key piece just will not budge from its place. This is likely because your lock isn’t in neutral position. Twist the saw blade a bit and it should solve the issue. If it still won’t budge, only then should you consult a licensed and insured locksmith to help you out, as the locking mechanism likely has a bigger issue. And, as always, it’s easier to prevent this issue with preparation: check your keys every few months to see if there are any cracks or major bending that would signal a possible break. Sure, its an easy enough issue to solve, but wouldn’t you rather be able to crash on the couch instead of performing surgery on a doorknob?