Come on does anyone know what they are talking about? I'm actually an old locksmith and yes even Kwikset still makes these locks with "contractor" pins or actually little balls that drop out once the owners key is used.. The contractor- builder gets his keys out and gives the new owners their keys.. They are not "masters" or fit any other house in the sub-division. All they ask is that you not use your "owner keys" until you no longer want the contractor entering the property. His key will no longer work once your key is inserted and rotated the first time it's used.. The locks can be rekeyed by any competent locksmith and they may be able to place the "balls" back in and let the contractor finish too!
I am *not* a locksmith, just a hobbyist. I have the original Kwikset Titan cylinder from when my house was built 18 years ago. Yes, it was changed out long ago, I just didn't throw the old one out. I have non-destructively disassembled and reassembled the lock a few times.
I have the original keys, and the lock belongs to me. I took it apart to see how it works. The "builder key" feature is well known and called something like ProtectoKey or some trade name. If you get the plug out of the lock and look at it, there are small holes next to the tumbler holes, but with slightly smaller diameter so the pins won't fit into them. They will line up with the tumbler holes when the key is turned counter clockwise about 30 degrees. The ProtectoKey function is implemented by putting 2-3 steel balls in one of the tumbler cylinders. The builder key opens the lock when the steel balls remain in the inner plug and the rest of the pins line up to the plug's shear line. The balls stay with the key-side as the cylinder turns. As others have said, when the owner's key is used the first time, the balls stay in the outer cylinder, and as the plug is rotated, they fall into the adjacent smaller hole. They stay there until the lock is disassembled, but upon doing so, the balls can be reset so the builder's key works once again.
In the case with my lock, 5 of the 6 tumblers have 3 pins, not just 2. That basically means that the cut of the builder's key is more like a master key, and need not be that close to the cut of the owner's key. The reason for this is probably so that, if someone like me figured this out, it would be harder to derive the cut of the real builder's key from examining just one lock cylinder. It also means that, even after using the builder's key, there can be a key that works as a master in the lock. To lay this out, I cut two additional keys in addition to the owner's key. One key works as a builder's master key, and is invalid once the owner's key is used. The next is a master key that works only after the owner's key has been used.
If you really want to see it, message me here and I'll put together a video demo, or just search for user bosnianbill on YouTube. I'm not him, but he does a lot of videos about locks in general, and he also has a low opinion of this design.
Because 5 of 6 tumblers have 3 pins, rather than 2, that means that for 5 tumblers, there are 2 different cuts that work in that position on the key. So even after invalidating the builder's key, there are 10 different key variations that can work in my lock. Oh yeah, and Kwiksets are notoriously easy to pick.
So yes, when moving into a new home, it is a good idea to replace the locks. Based on what I've learned, you probably want something more secure than Kwikset or Schlage, which are both very common and not terribly secure. That's my $.02, and it's worth what you paid for it.
Edit: I think I got the math wrong on the number of keys that will work. It might be as many as 32 key combinations.