I've been working for a property management company that runs a large apartment building. This kind of building presents a challenge: there are some doors which should be locked to the general public, but easily accessible to the residents.
This nifty lock is a good solution to the problem:
To open the lock, you simply punch in a short numerical code and then twist the silver knob just below the key pad. The lock can also be opened with a key in case the battery dies and the electronic parts stop working. The nice thing about this is that if you don't need to change locks or replace keys in order to keep out trespassers; you can just update the code every so often.
This is an excellent way to keep fitness rooms, laundry rooms, swimming pools and other amenities limited to use by the residents. In fact, it's great for anyone who regularly forgets their keys. You can even have two codes, with an "override" code for yourself and another code which you give out to friends or to the kids.
These locks sell for about $70 at the hardware store, so it's an inexpensive investment for the convenience it brings.