Many of these mechanical alarm watches have a steel post inserted in a hole in the steel back, and riveted in place. The post protrudes into a space in the mechanism adjacent to the alarm hammer, but not touching it. The case back is usually two-piece, with the back itself keyed to the case so it only goes on one way. An outer threaded ring is screwed down, holding the back in place. When the alarm trips, the hammer vibrates against the steel post. The sound is louder if the watch is OFF the wrist, but the muffled sound on the wrist is enhanced by the vibration.
Click to expand...