If you are concerned about lending out a key to somebody and then they go to the hardware store (or Fred Meyer’s) and copy it and then give it back to you without telling you that they still retain a copy, you can prevent this hypothetical problem with getting keys in a restricted keyway. This means that the profile of the key looking at it when pointed at your eye will be a different shape than fits in other locks. This also means that people can’t buy the same key blank, and thus can’t copy your key. If they had detailed information about the key they could copy it, or they could use a lost wax method or something to copy the key with a different medium than pre-cast key blanks. They will also have to go to a great deal more trouble to do so however. More trouble than simply pulling your door off with a tow hitch or blowtorching through your wall, etc.
The point of all of this is that with a restricted keyway, you can protect against a lot of scenarios involving security breaches that you can’t protect against if you have a common keyway. The costs are minimal: changing your keyway won’t break the bank. You are also not tied to my business. If you want you can pay another locksmith to change the keyway. If you want key copies however you have to come to me, and I maintain a database of who has what keys, and if you aren’t the same person who bought that key I will call the person in my database for that key. That is called key control management, and it means that nobody has the key unless you give it to them.
When I rekey people’s houses I always ask if they would like one knob or lever to be keyed differently to allow them to give out a key to workmen. On days when workers are expected, the deadbolt can be left unlocked and entry is permitted by unlocking the knob or lever. When entry by people without the common housekey is not desired, the deadbolt is left locked. This allows you to maintain a relatively safe and secure house though it still leaves you vulnerable to impressioning, picking and bumping. Criminals don’t usually employ these methods but it is worth thinking about to employ a keyway that makes it almost impossible to use a bumpkey or impressioning on. Such a lock is still susceptible to picking, but I also offer the upgrade of anti-pick pins which will defeat those of common criminal lockpicking skill. If your door is thick and your door frame is secure and your lock is grade 2, with a restricted keyway and anti-pick pins you are going to be nearly unassailable.
For those who are interested in the most reasonable prices, I can also give you a less expensive keyway that isn’t restricted, but is old and unused by most and only a locksmith will probably have access to the same key blank. Let me know!