Mechanical Principles › Complications › Chimes

THE ALARM

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1. Definition and purpose of the complication

The alarm watch is one of the oldest complications of mechanical watchmaking. Indeed, passing strikes already adorned the first mechanical clocks, well before these displayed the time on a Dial with Hands. This complication meets a universal need: signaling the programmed time by an audible sound signal.

Today, the alarm is featured just as much in Bracelet / Strap watches as in table alarm clocks. Particularly appreciated by travelers, it remains one of the most useful complications in daily life.

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2. An independent energy source

To function autonomously, the mechanical alarm mechanism requires its own energy source. That is why it is equipped with a Barrel dedicated, separate from the one that powers the main Time Movement. This Barrel is complemented by its own Wheel train and an independent speed Regulator.

This parallel architecture ensures that the striking mechanism does not disturb the running or the Autonomy of the watch. The Winding regular of the Alarm Barrel is therefore essential to the proper functioning of the Complication.

3. The Alarm Hand and the Release mechanism

The Alarm Hand is generally coaxial with the Hour Hand and positioned just below, on the Dial. Each is attached to its own Pipe wheel (Hour wheel) respectively, stacked one on top of the other. The Pipe wheel of the Alarm Hand is fitted with a Finger, while a corresponding hole is provided in the Hour Pipe wheel.

When the two hands align exactly — that is, at the set time —, the finger falls precisely into the hole. From that moment, the alarm’s barrel wheel moves vertically, thereby releasing the entire striking mechanism.

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4. The strike: hammer, gong and case middle

Once triggered, the mechanism releases the energy of the dedicated barrel into the wheel train. This train rotates at high speed and drives a hammer in a rapid oscillatory rhythm, regulated by a simplified form of escapement. The pace of the strikes determines the sound character of the alarm’s ringing.

Depending on the design, this hammer strikes a gong — a metal blade attached to the movement — or, in simpler constructions, directly the inside of the case middle. The gong produces a more melodious and sustained sound. On the other hand, direct striking on the case middle gives a shorter, drier signal, which is nevertheless often sufficient to wake the user.

5. Regulation / Adjustment of the ringing speed

Without regulation, the mechanism would consume the Barrel’s energy in a very short Time and the watch would ring too quickly. This is why a regulating flywheel is integrated into the Alarm Train (wheel train). In its simplest form, this flywheel is fitted with fixed vanes that create aerodynamic resistance, thus maintaining a slowed and regular rotation cadence of the Train (wheel train).

In more elaborate constructions, a variable Inertia flywheel is used. At high speed, the vanes move away from the Axis under the effect of centrifugal force, increasing resistance and slowing down the mechanism. Conversely, when available energy is low, the vanes move closer to the center, reducing resistance and allowing the Train (wheel train) to accelerate. This self-regulating device thus guarantees a ringing duration and regularity independent of variations in the Barrel’s energy.

6. The Regulation / Adjustment Crown and the ringing Switch

The Winding of the Barrel and the Regulation / Adjustment of the Release time are generally carried out by a dedicated Crown, separate from the main winding and time-setting Crown. In most constructions, this Crown also serves as a Switch: by pushing it or turning it to a defined position, the user activates or deactivates the Alarm chime.

In certain more elaborate designs, an additional Hand indicates the position of the Switch on the Dial, clearly signaling whether the watch is in chime mode or silent mode. This visual indication prevents any confusion when adjusting at night.

7. History and Evolution

The Alarm chime is attested as early as the 15th century on the first mechanical clocks, where it was notably used to call monastic communities to service. It is therefore one of the very first Complications of the history of watchmaking, even predating the Display of Time by Hands.

Its integration into the pocket watch, and later into the wristBracelet / Strap, required an extreme miniaturization of all its components — particularly the dedicated Barrel and the balance regulator. Today, several fine watchmaking manufactures continue to uphold this tradition.