One of the worst kinds of calls to get is the one where a customer is locked out because suddenly their deadbolt key just spins in the lock, failing to activate the latch – and they have no other way in. This means the tailpiece has broken – a malady that Kwikset locks seems to have more than any others due to the hollow metal tailpiece configuration that can suffer fatigue and break right off.
Before you pull out your drill and attempt to totally annihilate the plug so you can get to the latch itself, consider this little trick. This has worked for me on several occasions and has failed only once. You'll need to return later to install a trim plate, or better yet, stock a few different sizes in varying finishes in case you run into this. They can always be sold as extras after a while because a lot of people like the look of them anyway.

Drill a small hole in the door, about 3/16", right at the edge of the deadbolt where it meets the door. This can be done whether the door is wood or metal, because you're just going to drill into the cross bore area where the latch is. Place your mark at 12 o'clock and drill in a slightly downward angle, as though you were trying to hit the top of the latch. As soon as you feel the bit penetrate the skin of the door and you know you've entered the latch area, stop.

Now insert a stiff, slightly curved wire in the hole. It must be stiff enough to not bend readily. Coat hangar stock works, especially of the thicker wire variety (the cheap ones that bend if you look at them to long are not good for this!) It helps to put a little chisel edge on the end that's going into the hole, because you're going to fish for the hinge pin in the latch that moves up and back when the bolt is retracted. Keep fishing and keep moving the probe in a little up-and-back arc. When you catch the pin in just the right way, you'll retract the bolt and you can save the day and the deadbolt, too.

If you are new to locksmithing you might consider buying a kwikset dead bolt and studying the bolt, this will help you see in your eyes mind what you are fishing for.

TIP: It will be of great help if you can fashion a handle of some kind, such as out of a wooden dowel, to the wire. You might think about making this tool up while you have the time to do a good job of it, drilling a hole in a dowel that is barely the size of the wire and then epoxying the wire in place.

Consult the following diagram for an idea of the tool's shape.