The Complete Handbook of Alarm Clocks

Chapter 1: Understanding Alarm Clocks

The Alarm Clock as a Machine

An alarm clock is not a decorative object with a function; it is a simple machine with a single job. It must keep track of the current time accurately enough for its purpose, allow the user to specify a different time, and then produce a perceivable output at that specified time. This sounds trivial, but the engineering behind each of those three functions varies considerably across models. Understanding those variations will change how you select, use, and repair these devices.

The timekeeping element is the foundation of the entire device. In a quartz clock, this is a crystal oscillator that vibrates at 32,768 Hz, a frequency that is then divided down to one pulse per second. This pulse advances the stepper motor and the gear train or, in a purely digital clock, directly updates the display. In a mechanical clock, the timekeeping element is a spring-driven balance wheel or a pendulum, oscillating at a rate set by its physical dimensions and the tension of the mainspring. The accuracy difference is stark. A typical quartz movement will drift by a few seconds per month. A mechanical alarm clock will be doing well to hold accuracy within a minute over a week. Neither is a precise scientific instrument, but for an alarm clock, the practicality of the tolerance matters more than the absolute accuracy. If your device drifts by 30 seconds a day, you will notice when you rely on it