A clear sapphire caseback is not the only new feature that makes the latest Jaeger-LeCoultre Memovox distinctive from its predecessors. Jaeger-LeCoultre has also completely redesigned the striking mechanism, in part by attaching the alarm gong directly to the case side rather than the solid caseback.
This overriding change anchors the Master Control Memovox Timer and the Master Control Memovox, Jaeger-LeCoultre’s two newest updated and upgraded Memovox offerings.
Differentiating the two debuts, announced earlier this month, is a new alarm-setting mechanism within the Master Control Memovox Timer, and a subtly updated dial design with a date display that characterizes the Master Control Memovox.
Premiere alarm
Five years after Jaeger-LeCoultre introduced its first Memovox, which debuted in 1951, the Swiss watchmaker made history by developing an automatic version, the first automatically wound alarm wristwatch. Its chime is the audible result of the movement’s hammers hitting circular gongs, which have historically relied on the caseback for amplification of the chime.
The newest Memovox models feature gongs attached to the case itself rather than the (now-sapphire) caseback. While I haven’t had the opportunity to listen to these chimes directly, I suspect Jaeger-LeCoultre has taken great pains to retain the Memovox’s distinctive ‘school-bell’ tone with this update to Caliber 956.
The newly transparent sapphire back, which allows the wearer to watch the chime hammer in action, also exposes a new, open-worked pink gold rotor, decorated with Côtes de Genève to match the fine finishing on the movement plates.
The timer
On the new Memovox Timer, Jaeger-LeCoultre developed a timer that enables the owner to set the alarm, using the top crown, based on the number of hours that should elapse before the alarm rings.
Alternatively, the owner can set the alarm to sound at a particular time. The small hand with the Jaeger-LeCoultre logo indicates the elapsed hours-until-alarm. On the outer edge of the distinctive Memovox inner ring (here quite modern, engraved in bas-relief), a triangular marker points to the time at which the alarm will ring. 
Jaeger-LeCoultre will produce the Master Control Memovox Timer as a limited edition of 250 pieces. Price: $15,700.
Retro-style
For the Master Control Memovox, Jaeger-LeCoultre offers a subtly modernized version of its manual-winding 1950 Memovox.
Note its classical alarm and date display with a silvery sunray-brushed dial, applied triangular indexes, Dauphine hands with an updated blue seconds hand. As a nod to the past, Jaeger-LeCoultre has paired the Master Control Memovox with a new Novonappa calfskin strap that recalls the color of the first Memovox straps. Price: $11,600.
Jaeger-LeCoultre presents both these new Memovox models in the new 40mm Master Control case with an angled bezel, curved lugs and a contemporary combination of polished and satin-brushed surfaces.
Specifications: Jaeger-LeCoultre Master Control Memovox
Case: 40mm x 12.39mm stainless steel with satin and polished finishes, clear sapphire caseback, 50 meters water resistance.
Caliber: Automatic Jaeger-LeCoultre Caliber 956, displaying hours/minutes/seconds, date, alarm (Memovox function). 45-hour power reserve.
Dial: Silver sunray with date.
Strap: Novonappa calfskin.
Specifications: Jaeger-LeCoultre Master Control Memovox Timer (Reference: Q410848J, limited to 250 pieces)
Case: 40mm x 12.39mm stainless steel with satin and polished finishes, clear sapphire caseback, 50 meters water resistance.
Movement: Automatic Jaeger-LeCoultre Caliber 956 with hours/minutes/seconds, date, alarm (Memovox function), timer indication (hand with the JL logo), open-worked pink gold rotor, decorated with Côtes de Genève; power reserve: 45 hours.
Dial: Two-tone blue sunray dial, engraved numerals on the Memovox disc.
Strap: Blue leather