A couple of weeks ago in the middle of the night, something started chirping, then turned to a constant beep. I finally got out of bed to figure out where the noise was from, but it stopped before I could find it. Went back to bed, and of course it started up again a bit later.
It turned out that one of the buttons on my electronic deadbolt was intermittently pressing itself. The lock took this as someone trying to break the combination, and complained. I took the batteries out and went back to bed.
Later, 10 minutes on Google didn't turn up any parts available, and I'm trying to be extra frugal, so I decided to roll my own.
I found an old Princess-style phone in clear plastic--I could see that the keypad was a separate part, not molded into the case. With about 45 minutes work with a soldering iron and a multimeter, I had this mounted to my front door:
I did make sure the redial button doesn't actually work...