With a touch-pad lock, your pointer finger is your key. Just punch in a four-digit code and a battery-operated motor frees the latch. Some touch pads, like this LiNK dead bolt from Schlage, can be reprogrammed remotely with a smartphone, so the plumber can get in when you're not home. The battery has a three-year life and will alert you when it runs low; if it does die, the lock also works with a key.
About $200; Schlage