Alarm
A mechanical alarm that sounds at a preset time
What it is
A mechanical alarm wristwatch carries a second mainspring dedicated to the alarm striking train, wound independently from the going-train mainspring. The alarm time is set by turning a dedicated disc or using a second crown position. When the going train reaches the preset time, a release mechanism fires the alarm train, causing a hammer to strike a gong or the case resonating surface repeatedly until the alarm spring runs down; typically 20 to 30 seconds of striking.
History
Mechanical alarm wristwatches were developed in the 1940s. Vulcain introduced the Cricket in 1947; a favourite of President Eisenhower and subsequent American presidents; which achieved its distinctive buzzing sound by striking against the caseback as a resonating membrane. Jaeger-LeCoultre's Memovox appeared in 1950 (manual wind) and 1956 (the first automatic winding alarm wristwatch). The complication largely disappeared from catalogues as quartz phone alarms made it redundant; JLC, Vulcain, and a small number of independents continue producing it as a mechanical exercise rather than a practical convenience.
How it works
The alarm spring is wound via a second crown position or dedicated pusher. An alarm disc or cam on the movement is set to the desired time. As the going train advances, when the indicated position reaches the alarm disc's preset point, a lever trips the alarm train release. The alarm hammer strikes a gong or the case resonating surface in rapid succession until the spring runs down. The alarm cannot be stopped mid-sequence without physically deflecting the hammer.
Parts required
Second mainspring and barrel (alarm train), alarm disc with release finger, alarm hammer, alarm gong or resonating caseback membrane (as in the Vulcain Cricket), second crown or pusher for independent setting
In the catalog
Related
- Minute repeater: Strikes the time in chimes on demand
- Power reserve indicator: A display showing how much mainspring tension remains
