This is put together very quickly from bits I had already: an old CD writer from the days when all CD drives could double as standalone CD players. The main requirements being that it has a button dedicated to playing the CD and a headphone jack. This is powered by a nifty little PSU meant for powering hard drives while they are acting as external USB drives. Sound output is through a pair of normal PC speakers. The speaker not in the picture is pointing at the door so the sound can be better heard outside.
The sample was extracted from the movie using mplayer, edited with audacity and then burned to CD. Wires were soldered to the switch’s PCB pads and then connected to the wires going to the doorbell switch in place of the normal doorbell.
The effect is certainly spooky. The only problem is that the CD takes a good couple of seconds to spin up so there is a delay before the sound is heard. So the doorbell pushers tended not to associate the sound with their pushing the bell switch.
I was originally planning to use a very cheap mp3 player I got from ebay for this project, but it insists on playing in a loop so I’d have had to have rigged up a microcontroller or something to stop it once the sound has been played once. I didn’t have time, maybe next year.