Jaeger-LeCoultre Caliber 815 – Technical Overview from Document 1136_JLC

The Jaeger-LeCoultre Caliber 815 is a historically significant automatic alarm movement, introduced in the early 1960s and recognized as the first fully automatic wristwatch movement with an alarm function. Document 1136_JLC outlines the structure, core functions, and servicing guidelines for this pioneering caliber. It represents a major innovation in JLC’s Memovox line and laid the foundation for later developments such as Calibers 825, 916, and 918.

Technical Specifications

• Type: Automatic (self-winding), manual-wind capable for alarm

• Functions: Hours, minutes, central seconds, mechanical alarm

• Jewels: 17–18 (depending on variant)

• Frequency: 18,000 vibrations per hour (2.5 Hz)

• Power Reserve:

  • Timekeeping: ~45 hours

  • Alarm: ~18–20 hours

• Diameter: ~28.0 mm

• Height: ~6.5 mm

The movement is characterized by a dual-barrel system—one barrel powers the timekeeping train, the other powers the alarm mechanism. The rotor winds only the timekeeping barrel, while the alarm barrel is wound manually via a second crown.

Movement Features and Design

According to the schematics in document 1136_JLC, Caliber 815 features:

• A central rotor mounted on a jeweled arbor (not ball-bearing mounted like later calibers)

• A bidirectional winding system that transfers energy to the timekeeping barrel through a set of reverser gears

• A hammer and pin system to produce the mechanical alarm sound, striking against a resonance pin fixed to the inside of the case back

• Alarm time disc under the dial, adjusted by a second crown and engaged with the hour wheel cam

• A trigger lever and spring system that releases the hammer when the preset time is reached

The interaction between the alarm-setting disc and the timekeeping gear train is precisely timed to trigger the alarm without interfering with regular timekeeping.

Servicing Notes from 1136_JLC

The technical document provides servicing tips for:

• Rotor assembly and reduction gears: Clean and lightly lubricate the rotor pivots and reverser gears; inspect for wear on the jeweled rotor post

• Alarm hammer mechanism: Avoid lubricating the hammer pivot to maintain volume and clarity of the alarm strike

• Calendar-free layout: While the 815 has no date complication, care must still be taken with the dial-side assembly, especially the alarm-setting components

• Balance and escapement: Regulate beat error below 1 ms; target amplitude ~250°–270° (dial up, fully wound)

Final testing includes full alarm cycle testing and checking winding efficiency through rotor motion.

Use in Watch Models

Caliber 815 was used in:

• Memovox Automatic models from the 1960s

• Watches with two crowns: one for time and one for alarm setting/winding

• Stainless steel and gold cases, often 36–37 mm, with internal alarm resonator pins

• Classic JLC dials with alarm indicator discs (usually marked with an arrow or triangle)

Conclusion

The Jaeger-LeCoultre Caliber 815, as described in document 1136_JLC, marks a milestone in horological engineering—the first fully automatic movement with a mechanical alarm. It combines traditional Swiss watchmaking with functional innovation and laid the groundwork for all future Memovox calibers. For vintage watch enthusiasts, watchmakers, and collectors, it represents a cornerstone of mid-20th-century mechanical design. Proper servicing requires careful attention to rotor, hammer, and alarm systems to preserve its unique functionality and historical integrity.