“What’s that? A monopusher chronograph?”
“No, it’s an alarm watch, a Vulcain Cricket.”
“What do you mean? I don’t understand.”
“You wind it up and turn the pointer hand and pull the button and…”
One of the first vintage watches that fascinated me was a Vulcain Cricket. I could not believe that such a small mechanical object could make such a big sound. Alarms are a fun, interesting, and oftentimes affordable way to collect vintage watches. In this article I would like to introduce the curious history of the mechanical alarm watch.
Imagine you are in the Musee International d’Horologie. In a display case marked 1876, you see a magnificent filigree gold bracelet. In the center is a delicately carved cameo surrounded by large pearls, emeralds, and rubies. The cameo pulls open to reveal a tiny watch face with a keyhole for winding. What you won’t see is that when you set the alarm, this watch will discretely stick out a small pin, poking the wrist of the wearer. This elegant, yet painful mechanism is the first known alarm wristwatch. I suppose some male watchmaker thought that, like a corset or high heels, a woman’s wardrobe item should be pretty yet painful. Not surprisingly, it didn’t catch on.
Alarm wristwatches had a number of technological hurdles to overcome before becoming a practical everyday device. A minute repeater needs a pull on the slide to charge up the power reserve for the chiming mechanism before ringing out the time. An alarm needs to store up the power and hold it before letting it out at a preset time. The alarm either needs a separate mainspring that can run down without emptying out the power reserve for the timekeeping function or it needs to have a way to shut off the alarm quickly before the watch stops. You also need an indicator for the alarm set time that you can adjust easily. If you want to wear it regularly, the case needs to be sealed against dust and moisture which muffles the sound of the alarm. If you want automatic winding you have to find a way to have the hammer hit part of the case without getting smacked by the rotor and it would be better if it could power both the alarm and the timekeeping. The technical challenges are daunting, and the ways in which various manufacturers tackled them form the story of alarm wristwatches.
The Forgotten Alarm Watch: Eterna 1914
Watch people know that Alberto Santos-Dumont took flight in 1904 wearing the first wristwatch made by his friend Louis Cartier. A little known fact is that only ten years later in 1914 Eterna made the first series produced alarm wristwatch. The initial version was a transitional piece between pocket watch and wristwatch. It looks like a trench watch with its small, soldered on lugs and thick application of radium paint to the cathedral hands and Arabic numerals. The pocket watch heritage is also seen by the pin set mechanism by which a small pin at 4 is pressed down in order to set the time. The second series got rid of the pin set and went to a more modern crown pull mechanism.
The jumping on the bezel is a signal that the bezel rotates to move the alarm setting hand. You can rotate the bezel clockwise or counterclockwise as indicated by the bidirectional arrow on the dial. Other notable features were the inner caseback that has the appearance of a dust cover. It doesn’t keep out much dust though since it has a hole to allow for an on-off switch but having two casebacks helps amplify the alarm sound. There is no space in the movement for a seconds hand. There is a single mainspring and the power reserve is preserved by an alarm holding wheel that stops the alarm after seven seconds.
Although it gets no love from the Instagram crowd, the Eterna 42 403 is a critical piece in the development of the alarm wristwatch. It represents the transition from pocket watch alarm calibers to wrist alarms. It had an unusual bidirectional alarm setting bezel. It had an early version of a double caseback. Most importantly, the alarm holding wheel was crucial in preventing the mainspring from running down when the alarm rang. Some version of this mechanism exists in all subsequent single mainspring alarm wristwatch calibers. Much like John Harwood’s automatic winding bumper system would be overshadowed by Hans Wilsdorf’s adoption of the Rolex Perpetual 360 degree rotor system, the innovative Eterna alarm wristwatch was overshadowed by later, more user-friendly alarm systems. The Eterna caliber was produced until 1946.
An interesting historical note that that A. Schild, the company that later manufactured the ubiquitous AS 1475, was founded by Adolph Schild. He not only worked for 30 years for Eterna as its technical director but also was the brother of Urs Schild, Eterna’s founder. The two companies were reunited in 1979 when A. Schild was merged with ETA. You might say that the Schilds were the first family of alarm watches!
1947: Enter the Vulcain Cricket
CHIRP CHIRP CHIRP
Crickets produce sound by rubbing a “scraper” on one front wing against a “file” on another. The central wing contains a “harp” which is a bit of hardened, horn-like resonating membrane. The sound is further amplified by the resonance between the wing and the body wall.
Paul Langevin was a French physicist notable mainly for three things: developing a submarine detection system using ultrasound, being an outspoken anti-Nazi in Vichy France, and having an affair with Marie Curie. His claim to fame in the watch world was his friendship with Vulcain technical director Robert Ditisheim. According to Vulcain, it was their discussion of the sound production mechanism of a cricket which led to the development of the double caseback. This was the key invention which allowed for a loud alarm within a water resistant case that was the first practical alarm wristwatch.
The Vulcain Cricket has a hammer which strikes a pin that is attached to an inner stiffened membrane acting like a cricket’s “harp.” The outer caseback acts as the “wing” by creating a resonating chamber to amplify the sound. The edges of the outer caseback have holes to allow the sound to travel outwards similar to the center hole of a violin. The double caseback was so critical to the success of the Cricket that it was patent protected in 1949. Numerous lawsuits were filed against imitators, first against JLC then against an astounding 62 other watch companies! It was not until the patent expired that other alarm watch makers could produce double caseback watches without paying a royalty to Vulcain.
The Vulcain Caliber 120 uses two separate mainsprings for the alarm and the timekeeping function. The Vulcain Cricket had an innovative mechanism that permitted a single crown to wind both mainsprings. The timekeeping function was powered by turning the crown one way and the alarm mainspring was powered by turning the crown the other way. The alarm was wound in the more intuitive clockwise direction because it was thought that the alarm would need multiple windings per day as it was used. The separate alarm mainspring allowed for a rather long alarm time of 30 seconds. The Caliber 120 also incorporated an innovative balance wheel mounting called the Exactomatic that preserved amplitude in vertical positions, improving accuracy. A final innovation was that the time was able to be set forward only to prevent damage to the alarm mechanism, helping to render the alarm “idiot proof.”
The reliability, ease of use, loud and effective alarm, and distinctive styling led to Vulcain becoming synonymous with the Cricket alarm watch.
A number of American presidents wore the Vulcain Cricket such as Eisenhower and LBJ, leading to the nickname “President’s Watch.”
A number of Cricket variations are notable for their differing functions.
The Cricket Calendar (Caliber 401/402). You may have seen some funny looking Vulcain Crickets that have a date window, a crown at 2:30, and an often rounded button at 3:30. These Cricket Calendars were designed as a lower priced option with a non-quickset date and a single mainspring. Due to the single mainspring, the alarm duration was only 10 seconds. The duration of the alarm was limited with the use of an alarm holding wheel as it was in the Eterna 42 203. The main difference with the later 402 is that the 401 requires that you wind the timekeeping function to make the crown “pop out” and activate the alarm whereas the 402 allows for the crown to be pulled out for alarm activation.
The Golden Voice. Robert Ditisheim found in his many pre-Cricket prototypes that the most beautiful sound came from a gold membrane. The woman’s Cricket received the name by always using a 14K gold membrane regardless of the case material. The Caliber 406 squeezed the features of a Caliber 120 into a movement 8.3 mm more narrow and 0.35 mm thinner. The short alarm time of 7 seconds reflects the small alarm mainspring rather than an alarm holding wheel. Accuracy in a small mechanism was maintained using the Exactomatic balance. A lot of technology was put into a watch that, amazingly, measured only 22 mm in diameter!
The Nautical is Vulcain’s dive watch alarm. The Nautical is instantly recognizable by its large size and complex dial. The diameter is 42 mm and it has a height of 17.7 mm. The inner membrane is reinforced with a thick inner lid to prevent collapse from water pressure. The plexiglass crystal is also extra thick. The crowns, a main crown and second crown at 4, are recessed.
The 1961 version has decompression tables and an overall more conventional case and “sea urchin” dial.
The 1969 version has a tonneau style case which gives it a bulkier appearance with orange accents and an inner rotating bezel replacing the decompression tables.
Over time there were a number of Cricket variations either produced by Vulcain or by various partners who licensed either the technology or the name.
The Sensialarm. Utilizing the Caliber 120, it differs in that it lacks the double caseback so that it has a quieter alarm.
Other brands licensed the Caliber 120 including Hamilton.
Waltham Alarm. Licensed the Caliber 401/402.
Vulcain Alarm. Sadly, the American distributor for a time licensed the Vulcain name to distribute watches utilizing the AS 1475. These are easily distinguished by the double crown.
Vulcain became part of a larger conglomerate called MSR run by Revue in 1961. Thommen Cricket. The Vulcain name was discontinued in 1986 but the alarm calibers were reissued under the Revue Thommen name. The Vulcain brand was spun off and went bankrupt after a short period and was later revived as the modern Vulcain. The discontinuity of the brand and multiple licensing agreements may have contributed to the lesser popularity of the Cricket compared to the JLC Memovox and Tudor Advisor.
The Competition: Jaeger-LeCoultre Memovox
JLC had already built a handful of alarm watches in 1929 but their first series production Caliber 489 Memovox was issued in 1949, two years after the Cricket. The patent protection of Vulcain’s double caseback technology was upheld in court so the Memovox had a noticeably quieter alarm sound without the outer perforated resonating caseback. The early Memovox tried to compensate for this deficiency with a rather odd lug arrangement. The band was held in place by two hollow tubes, open on one side to admit the band, which were welded to the underside of the caseback rather than to the side of the case. It therefore held the caseback off the wrist so that the resonating caseback was not muffled by contact with the skin. While providing an interesting art deco look, the lug tubes were perhaps not the most practical or comfortable solution.
Later models had delicate, swept back lugs to raise the watch partially above the wrist before abandoning the concept and settling into more conventional cases with the corresponding diminished alarm volume. This is made obvious when comparing the loudness of the alarm of a vintage Memovox on the wrist versus in the hand.
Two other distinguishing features are notable in the Caliber 489. A double mainspring was also used but the timekeeping and alarm functions were separated into two crowns with the time at 4 and the alarm at 2. This was perhaps a more intuitive setting function and its success is evidenced by all subsequent JLC alarm calibers following the same design as well as the ubiquitous AS 1475. The other notable feature is that the alarm setting was via a central disc rather than a pointer hand which lent it a distinctive appearance. Using the separate alarm mainspring, the Caliber 489 could sound for 20 seconds.
JLC advanced alarm wristwatch technology perhaps more than any other manufacture. After a few iterations on the 489, the Caliber 911 was introduced in 1962 with a date indicator while preserving the basic architecture and ease of use. This no compromise approach is in contrast to Vulcain’s decision to create a cheaper, simpler caliber for their date function watch which had a shorter alarm time and issues with alarm setting.
In 1956, 42 years after the introduction of the wrist alarm by Eterna, JLC finally introduced automatic winding with the Caliber 815, known as the 825 after the addition of a date. Although it seems like a long wait, automatic winding would not appear in chronographs for another 13 years. The problem with a conventional 360 degree full rotor in an alarm caliber was that the alarm hammer needed to strike against a pin attached to near the center of the caseback to produce the optimal sound volume. Striking against a tone spring at the edge of the case was another option that would require a movement redesign to relocate the hammer, and striking the side of the case did not produce a sufficiently loud alarm. JLC came up with a 270 degree bumper automatic system with a wide, curved cutout. The caseback pin could drop through the cutout and be struck by the hammer and the bumper could go around it while winding. This was an innovative, unique, and rather ingenious solution.
13 years later in 1969 JLC introduced a 360 degree full rotor automatic movement in the Caliber 916. Again, the issue of the centrally mounted caseback pin was solved in an innovative fashion. The central rotor was mounted with three screws and the center of the rotor itself was left empty to fit the caseback pin. The hammer was thus directed against the pin at the exact center of the watch, preserving loudness and allowing for the more efficient winding of the rotor compared to a bumper. The date had a semi-quickset function with back and forth movement of the hands between 9 and 12. The beat rate was also increased to a modern 28,800 bpm, giving this caliber the nickname of “Speedbeat.”
The JLC Memovox caseback is worth commenting on further. JLC resolutely refused to put a double caseback on their alarm watches until the Polaris. Even the JLC Deep Sea Alarm came with an outer screw down ring. The early versions had a snap off back. Through most of its history, JLC alarms had a screw down outer ring to secure the caseback. The caseback pin fit into either a slot in a manual wind caliber but or a groove in an automatic caliber. This meant that a screwdown outer ring was necessary in order to prevent breaking off the caseback pin during rotation of a screwdown caseback. A broken off pin is a sign that someone tried to rotate the caseback. The 916 caliber allowed for a screw down caseback because the slot for the caseback pin was located in the center of the movement.
One of the most distinctive Caliber 916 Memovoxes is the “Snowdrop.” A UFO shape, hidden lugs and a monocoque case are characteristic of this reference. The movement drops in from the front and the bezel screws down on top. No detachable caseback is present in this reference.
Another funky one was the egg shaped Memovox GT. These came with 825 bumper or 916 Speedbeat movements. The bumpers had the screw down ring and the Speedbeat had a screw down caseback.
A couple of references are notable mostly for the central discs. Please use caution when examining these references as the discs can be faked.
The Memovox World Time. Including a rotating disc allowed for an inexpensive worldtime function.
Memovox Parking. The central disc indicator was conducive to developing a parking timer. The arrow was marked with a blue “P” and indicators for 2 hours, 60 and 30 minutes could be aligned with the minute hand to use the alarm as a countdown timer.
American Lecoultre. The American distributor of JLC sometimes matched American cases to JLC movements. The caseback is usually marked “Cased and timed in USA by Lecoultre.” These tended to be smaller and gold-filled and can often be found for a lower price than a Jaeger Lecoultre.
Deep Sea Alarm. A very valuable dive alarm. One was famously found for $5.99 at a Goodwill in Phoenix in 2015 as reported by Eric Wind in Hodinkee.
Polaris. A large 42 mm dive watch, the Polaris had an inner rotating bezel controlled with a third crown, a thick domed plexiglass crystal, an automatic bumper movement, and a double caseback. An interesting comparison of the original, more rounded and less boxy compared to the service crystal was given by Blomman Watch Report. The Polaris II was equipped with a Speedbeat movement and was larger at 44 mm and more colorful.
The Underappreciated yet Ubiquitous AS 1475
If you see an alarm wristwatch with two crowns at 2 and 4 and it is not a JLC, chances are that it contains an AS 1475. Released in 1954, it was a latecomer to the wristwatch alarm caliber party but the robustness, loudness, reliability, and mass production saw it deployed across a number of brands. An incredible 1.4 million AS 1475 and related calibers were produced, dominating the wrist alarm market. Manual wound AS alarm calibers can be identified by a characteristic tricorner central bridge. The two crowns control a two mainspring system with the alarm function at 2 and the timekeeping function at 4, similar to the JLC calibers. There is an alarm pointer hand instead of a disc. The alarm strikes for 15 seconds and is rather loud, especially with a double caseback. The hammer strikes the caseback pin in the bottom left as marked by the yellow arrow. Other calibers also share two crowns but the position of the caseback pin is also characteristic of the AS 1475.
AS continued to push forward in advancing alarm caliber technology, first by adding a date function to their base caliber in 1956, a full six years before JLC would do the same with the Caliber 911 in 1962. Also hot on the heels of JLC, AS produced a high beat version of their alarm calibers in 1970, one year after the JLC 916. Granted, AS used an intermediate beat rate of 21,600 bpm rather than the Speedbeat’s 28,800, but it was still a remarkable achievement for the time. However, no quickset or semi-quickset date function was yet available.
The later AS 5001, nicknamed the “Brainmatic” increased the beat rate to a modern 28,800 and added hacking seconds. Perhaps stimulated by competition with the Seiko Bellmatic, the Brainmatic quickly evolved through the 1970’s. AS first added 360 degree rotor automatic winding for first the timekeeping mainspring then for the alarm mainspring as well. The winding was separated by direction so that clockwise or counterclockwise rotation of the rotor would wind the two mainsprings separately. The next step was to add a quickset day then a quickset day date. This culminated in the AS 5008 of 1973, a 30.4 mm diameter 7.9 mm high movement with full rotor winding of both mainsprings, a high beat movement, hacking seconds, and a quickset day date. This was arguably the pinnacle of vintage alarm watch technology. However, the alarm lost some loudness because the hammer was moved to the periphery to avoid the rotor and struck a tone spring instead of a centrally located caseback pin. Pro tip: if you see a date date alarm but it’s not a Seiko Bellmatic, you are looking at an AS 5008.
As mentioned in the Eterna section, A. Schild was the brother of the founder of Eterna and served as their technical director for 30 years. It was merged with Eterna’s movement producer ETA in 1979, 83 years after the initial separation.
The quality of the AS 1475 was evidenced by the use by Rolex in the Tudor Advisor. As was typical for the Tudor line until recently, a third party movement was put into a Rolex case with a Rolex dial.
Tudor Advisor 7926 was issued in an Oyster case (1957)
A more rare variant was the 1537, a dressier version with thin lugs and a smaller 33 mm size.
Tudor Advisor 10050 had a double caseback after the Vulcain Cricket patent expired (1969). The 3745 movement is based on the AS 1475 and has the characteristic tricorner bridge.
Girard Perregaux had a distinctive modification of the AS 1475 with a semicircular alarm indicator window from 5 to 7.
The Russian Poljot alarm caliber was based on the AS 1475 architecture as evidenced by its construction with the characteristic tricorner bridge. One jewel was added, presumably to assert Soviet superiority.
Citizen also used a modified AS 1475 movement. The jewels were increased to 21 and the movement was made larger. The shape of the tricorner bridge was slightly altered as well.
Japan’s Champion: The Seiko Bellmatic
Seiko expert David Flett has already given a definitive history of the Seiko Bellmatic here along with a guide to the main references. I will try to place the caliber into a larger context.
The Bellmatic was initially released in 1966 in Japan. The 4006A was the main caliber with a day date. The 4005A was released for about a year starting in 1968 and was day only. The 4006A initially had 27 jewels, and then decreased to 21 then 17 jewels. This was likely to avoid American tariffs on movements with more than 17 jewels. The differences between the various jeweled movements are minor and I will not go into them in great depth. Suffice to say that the earlier movements, typically 27 or 21 jewels, came with a longer tone spring and less bulky cases so the alarm was brighter, louder, and more clear.
The most distinctive feature of the Seiko Bellmatic from the dial side is the absence of a central disc or an alarm hand indicator. In a great improvement in legibility, an indicator arrow mounted on an inner rotating bezel is used to set the alarm. Another feature somewhat reminiscent of the Vulcain Caliber 120 is that a system with two mainsprings is controlled with a single crown and button rather than the usual two crowns. However, the date is quick set with a push of the button, the first true quickset date among alarm watches and the only quickset date other than the Omega SL 980 in 1969 and the AS 5007/5008 in 1973. Recall that the JLC 825 had a semi-quickset date done by moving the hands back and forth from 9 to 12. The day feature has a semi-quickset function done by moving the hands back and forth from 10 to 2. The crown in position 0 winds the alarm mainspring, in position 1 sets the alarm by turning the inner bezel, and in position 2 sets the time. In typical Seiko fashion, the timekeeping mainspring is wound through the 360 degree automatic rotor using the magic lever system with no hand winding possible. Due to the automatic rotor, the hammer is placed at the edge of the movement and strikes a tone spring which leads to a fairly loud and pleasant sounding alarm. This will sound for 10 seconds.
It is worth noting that in 1966 when Seiko released the Bellmatic, JLC’s most advanced alarm caliber was the 825, which had an inefficient bumper winding system and a nonquickset date.
The Seiko Bellmatic is a fun and affordable alarm watch to collect due to its variety of dial types and case styles. The technology was far ahead of its time and in terms of functions it remained the most advanced alarm watch caliber in the world until the AS 5008 seven years later.
The Omega Memomatic
A latecomer to the alarm game, Omega waited until 1969 before releasing a wrist alarm caliber. The SL 980 was a highly advanced movement that some consider to be one of the last complicated calibers released by Omega before they had a dark period during the quartz crisis. There were two main innovations.
The first was automatic winding of the timekeeping and alarm functions through the use of a single barrel. I think it deserves emphasis that the SL 980 was the first vintage caliber that allowed for automatic winding of both functions and was the only one other than the AS 5008, released 4 years later. A more advanced form of the old alarm holding wheel system from the Eterna was used to limit the alarm to 10 seconds. The 360 degree rotor automatic winding system was efficient enough that the alarm could be fully powered after an hour on the wrist, or topped off with manual winding. Using a single barrel meant that the winding was more efficient than the AS 5008, in which the rotor wound each mainspring by turning in the other direction. An hour on the wrist was enough to recharge the alarm, which could also be topped off with hand winding.
The second innovation was alarm setting that was accurate to the minute. The SL 980 remains the only caliber capable of this level of accuracy. The watchmaker tolerances were +/- 4 minutes for the alarm setting. This feature requires the addition of a second indicator to indicate the alarm minute. The SL 980 used a system of double discs which have an arrow on the outer disc to indicate the hour and two parallel lines on the inner disc to indicate the minute. This was special enough that the alarm setting function to the minute was removed for the Lemania 2980. Clients for the 2980 included Enicar, Nivada, Sicura and others, and are distinguished from the SL 980 by the lack of a minute set disc. The Lemania 2980 was also nickel plated rather than the more function and aesthetically pleasing copper plating characteristic of Omega calibers.
A third advanced feature which the SL 980 shared with the earlier Seiko Bellmatic and later with the AS 5007/5008 was a quickset date function. This was activated by pushing a depression at 3. The alarm itself has a moderate volume. Due to the automatic 360 degree rotor the hammer strikes a tone spring at the edge of the movement. The bulky 1970’s cases may also contribute to the slightly muffled sound.
Although the SL 980 was produced for only 5 years, its technical innovations give it a place as a candidate for the most advanced vintage alarm caliber ever produced along with the AS 5008.
In additional to the cushion case, they also came in an egg shaped Flightmaster style case.
Not all watches with two crowns had a AS 1475 or JLC movement. The Bulova 11 AERC may initially look like the more commonly found calibers but in fact is rather different. The top crown winds a single mainspring that powers both the timekeeping and alarm. The crown at 4 sets the alarm and activates it when pulled out. Power is conserved in the single mainspring by the now familiar alarm holding wheel. The alarm sounds for a surprisingly long 15 seconds with only a few winds of the movement. This attests to the efficiency of the winding mechanism and energy delivery to the alarm function. The squiggly alarm hand is characteristic of the Bulova alarms.
The Venus 230 is a good example of an alarm watch with an on off indicator window. Green indicated that the alarm was active and red that it was inactivated. The movement utilized a single, rather long mainspring that allowed for a power reserve of 60 hours without alarm usage. Another practical feature is that when the alarm is active neither the time nor the alarm time can be set by the two crowns, preventing an accidental alarm.
Another oddball with a distinctive dial is the Baumgartner BFG 90. Like the Vulcain 120, this movement has two mainsprings wound by a single crown. However, instead of turning the one one way to wind one mainspring and then the other to wind the second mainspring, this watch winds both mainsprings in the same direction. There is a slipping bridle that activates when one mainspring is fully wound, similar to the way an automatic watch is preventing from breaking the mainspring as it continues to be wound on the wrist or by hand. The problem is that there is no way to tell that the mainspring is fully wound. The Baumgartner added simplified power reserve indicator windows located at 2 for the timekeeping mainspring and at 4 for the alarm mainspring. There is also a shut off button on the side of the case and a turning bezel to set the alarm time by turning counterclockwise. This is a truly innovative yet affordably made caliber!
The Hanhart San Souci had some fun features worth mentioning. A single mainspring movement, it initially had a single crown. The first generation set the alarm time by a rotating bezel. However, to shut off the alarm one had to pull the crown and push it back down or turn the alarm setting bezel. A later series added a shut off button at 9. A cool feature is the folding sound bridge. This sat on top of the caseback lifted the watch and prevented muffling by contact with the skin. It also doubled as a kickstand to convert the wristwatch into a travel alarm clock.
The Pierce DuoFon had a unique feature of being able to set the volume of the alarm. A crown at 4 controlled a movable pin which could connect or disconnect the hammer to a tone spring, altering the volume of the alarm. A red indicator on the dial would alert the owner to how loud the alarm would sound.
I hope this article helps to expand the appreciation of the vintage alarm watch. The various ways in which the manufacturers handled the technical hurdles of overcoming issues with water resistance, automatic winding, power reserve while maintaining a loud and robust alarm mechanism are the heart of the story. Many calibers were not discussed here but I tried to assemble a lot of information and photos in one place. If your favorite vintage alarm is not included or if you spot an error please contact on Instagram @watchmedtime.
The bulk of the material and inspiration for this article comes from Michael Philip Horlbeck’s book “The Alarm Wristwatch: The History of an Undervalued Feature.” All sorts of rare and wonderful alarm watches and calibers are described and depicted in great detail. If you have a serious interest in alarm watches, you need a copy which you can buy here
Ranfft Watches is an indispensable guide for watch calibers. Find it here
Check out David Flett’s definitive guide to Seiko Bellmatics here
I Know Watches has a great guide on Seiko Bellmatics here
Blomman Watch Report is a well-researched blog specializing in vintage and modern JLC. Check out their series on American Lecoultre here
Timepiece Chronicle has a good article on vintage Tudor Advisor variants here
Desmond Guilfoyle wrote the definitive guide on Omega Memomatics here
Thank you to Patrick Rosshart at Hanhart for providing pictures of the rare San Souci.