Mechanical Principles › Complications › Chiming Mechanisms

THE PASSING STRIKE

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1. Definition and general principle

Passing strike is a complication that automatically chimes the hours, without user intervention. Unlike the minute repeater — which indicates the time by chiming on demand —, it is triggered autonomously over time, at the passing of each predefined interval (each hour, or even each half-hour or quarter-hour). Together with the Alarm, it is one of the oldest forms of chiming watchmaking complications.

In its simplest form, the passing strike strikes one or more chimes at each full hour, without however indicating its numerical value. More elaborate variants also chime the half-hours, or even the quarter-hours, each interval then being distinguished by its own sound code.

2. Striking modes: hours, half-hours and quarters

The passing strike comes in several variants depending on the intervals struck. The most common version strikes only the full hours: a single strike per hour is the most common and energy-efficient form. Some watches also strike the half-hours, adding a useful intermediate marker.

The most elaborate constructions also strike the quarter hours, thus providing more precise time information. In this case, a striking code distinguishes the three intervals: for example, one low strike and one high strike for the hours, one high strike for the half-hours, and one low strike for the quarters. This sound hierarchy allows for punctual auditory reading, without consulting the Dial.

3. The chime: one or two tones

The strike is produced on one or two chimes, blades or metal wires wound around the Movement and struck by a hammer. With a single bell, all strikes sound in unison. With two bells tuned differently, it becomes possible to distinguish the intervals by the pitch of the sound.

In the common case of watches striking hours and half-hours, the hours are struck on both bells simultaneously or successively, producing a full sound. The half-hours, on the other hand, are struck on only one bell, producing a shorter, lighter sound. This acoustic distinction is immediately perceptible, even without looking at one’s watch.

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4. The release mechanism

The release of the striking mechanism is provided by the motion work, which controls the strike at regular intervals. A Cam attached to the Hour wheel releases, at each full hour, a lever holding back the striking mechanism. As soon as this lock is released, the striking Train (wheel train) runs free and controls the hammer.

This Release is entirely passive: the continuous rotation of the Movement is enough to arm and release the mechanism.

5. The energy source: the main Barrel

Unlike the mechanical Alarm — which requires a dedicated Barrel to produce a prolonged ringing —, the Passing strike draws its energy directly from the Movement’s main Barrel. Its energy consumption is indeed very low: one or even two strikes per hour are enough, without significantly drawing on the Power reserve.

This energy saving allows the Complication to be integrated without making the Movement excessively heavier or more complex.

6. The Switch: slide lock and Pusher

For obvious comfort reasons — particularly at night — any passing strike mechanism must be able to be deactivated. Two solutions are commonly used for this purpose. The slide lock is a sliding lever, usually positioned on the Case middle or on the Case back. By sliding it, the user locks the Release lever, thereby preventing the striking Train (wheel train) from being freed.

The Pusher performs the same function in a more compact form, often integrated into the Case middle alongside the Crown. In some designs, a small Hand or a window on the dial visually indicates the position of the switch — striking mode or silent mode — thus avoiding any uncertainty.

7. Distinction from strike on demand

The passing strike and the minute repeater both belong to the family of striking complications, but their logic is fundamentally opposite. The passing strike is automatic: it is triggered without intervention, at fixed times. The minute repeater, on the other hand, strikes the exact time on demand, in response to the activation of a pusher or a sliding mechanism.

Therefore, these two complications serve distinct purposes. The passing strike suits those who wish to follow the time without looking at their watch, for example during a meeting. The minute repeater, on the other hand, is valuable in total darkness, allowing the exact time to be known down to the minute. These two approaches can nevertheless be combined within a single Movement.

8. History and evolution

The passing strike is intimately linked to the very origins of mechanical horology. As early as the 14th century, the first church and steeple clocks struck the hours on a bell, well before any Display by Hands on a Dial existed. The strike was not a complement to the display: it was its very first form, meant to mark the rhythm of communities’ lives.

Its transition to the pocket watch, then to the wristwatchbracelet, required a progressive miniaturization of all its components — hammer, bell, cam and counting mechanism. In the 20th century, the passing strike became more widespread in affordable watches, thanks to simplified constructions using a single bell. Today, it remains a benchmark in the family of sound complications.