Description
Citizen Hisonic tuning fork wristwatch
MADE IN JAPAN
The Citizen Legacy: A Pioneer of Precision
Founded in 1918, Citizen is now one of the largest watch and movement groups in the world. The Japanese brand is known for its highly accurate and reliable Eco-Drive solar-powered watches. The Citizen group owns Bulova, Alpina, Frederique Constant, and Arnold & Son, as well as movement manufacturers Miyota and La Joux-Perret.
About the Hisonic Line
In 1971, Citizen entered a licensing partnership with the American maker Bulova to bring “tuning fork” watch technology to Japan for the first time. Bulova had pioneered the technology in 1960 with the Accutron, using an electrically driven tuning fork resonator — vibrating at 360 Hz — in place of a conventional balance wheel, driving the hands through a tiny index wheel and pawl. Citizen manufactured the movements themselves under license, badging the resulting watches “Hisonic.”
The Hisonic line launched with the day-only caliber 3701, followed by the day-date 3702, and Citizen went on to build the family in parallel versions — calendar calibers in the 3700 series, date-only calibers in the 3710 series, and no-calendar calibers in the 3720 series, among them the 3721A fitted to this watch. All are versions of Bulova’s Accutron 218 movement, the 3721A corresponding to Bulova’s own caliber 2180G, and Citizen priced the line as a genuine premium offering: Hisonic models sold for 38,000 to 60,000 yen in 1973, well above an ordinary mechanical watch of the day. Around a million were made before production ended in 1977, when quartz crystal timekeeping made the tuning fork’s famous “hum” obsolete almost overnight.
About This Watch
This example is a Citizen Hisonic from January 1975, reference 3721-375076 Y, serial 50100522, powered by Citizen’s caliber 3721A tuning fork movement (15 jewels) — Citizen’s licensed version of the Bulova Accutron mechanism. Rather than a balance wheel or quartz crystal, the movement drives an electrically excited tuning fork that hums at 360Hz, indexing the hands through a tiny pawl-and-wheel mechanism for the smooth sweeping seconds hand tuning fork watches are known for. It carries a teal sunburst dial signed “CITIZEN TUNING FORK HISONIC,” a clean three-hand layout with no date complication, on a vintage stainless steel mesh bracelet.
Technical Specifications
- Brand: Citizen
- Line: Hisonic
- Reference Number: 3721-375076 Y
- Movement: Citizen caliber 3721A tuning fork (15 jewels), licensed from Bulova’s Accutron mechanism
- Serial Number: 50100522
- Production Date: January 1975 (from serial 50100522)
- Case Material: Stainless steel
- Case Diameter: ~38mm (visual estimate, not calipered)
- Dial: Teal sunburst, applied baton markers, three-hand with no date complication
- Crystal: Acrylic crystal
- Case-back: Screw-down stainless steel, engraved with reference and serial numbers
- Country of Manufacture: Japan
Condition Report
The dial and indices are clean and glossy with strong, even teal color and no notable fading or staining. The case shows honest, light wear consistent with its age – a few fine surface marks on the lugs and case sides, with no dents or heavy over-polishing evident. The stainless case-back is engraved with the reference and serial numbers, fully legible. The stainless steel mesh bracelet is present and functions correctly; the clasp is unsigned, so while the bracelet is period-correct, we can’t confirm it’s the factory-original bracelet for this specific watch (see sizing in the product photos).
This watch has recently been serviced by a professional watchmaker and keeps good time.
Comes complete with vintage steel bracelet*.
(*)Note: Stock bracelets are often shortened by previous owners and may not fit you(see bracelet size in the product images). We match the strap to this watch’s lug width, so there is nothing for you to measure — just pick a padded leather strap for Citizen from the options at the top of the page.
This watch ships from 🇺🇦 Ukraine with tracking number
Why Collectors Want This Watch Today
Tuning fork watches are a genuine curiosity on today’s vintage market — a technology that ran from 1960 to the late 1970s before quartz replaced it, and one most collectors have read about but rarely held. Citizen made the Hisonic in quantity, so this is not a rare watch, but it is an unusual one, and this example pairs the tuning fork movement with a teal dial — a bolder color than the silver and champagne dials most commonly seen on 1970s Citizens. Hold it to your ear and you can hear the tuning fork’s characteristic hum, and watch the seconds hand sweep smoothly rather than tick — something no ordinary mechanical or quartz watch can replicate. It’s a fitting piece for anyone who wants a slice of horological history that looks as distinctive as it sounds.
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We guarantee the item you receive looks and works exactly as advertised — or your money back.
Citizen lug-width matched leather straps — 18 / 19 / 20 mm
About the watch factory
The Spirit of Innovation: The Citizen Legacy
Founded in 1918 with the mission of creating timepieces that are “Citizens” of the world, the Citizen Watch Company has spent over a century redefining the boundaries of horology. From its origins as the Shokosha Watch Research Institute, the brand has remained steadfast in its philosophy: “Better Starts Now.” This belief—that it is always possible to make something better—transformed a local Japanese workshop into a global powerhouse of precision and craft. By controlling the entire manufacturing process in-house, from the individual components to the final assembly, Citizen ensures an uncompromising standard of quality that few manufacturers on earth can match.
What truly sets Citizen apart is its relentless pursuit of pioneering technology paired with environmental consciousness. The brand made history by introducing the world’s first light-powered analogue watch — the Crystron Solar Cell of 1976, the technology Citizen later branded Eco-Drive, which eliminated the need for battery replacements and forever changed the industry’s approach to sustainability. Beyond its eco-friendly milestones, Citizen’s history is decorated with “world firsts,” including the first professional diving watch with an electronic depth sensor and the most accurate satellite-synchronized timekeeping systems. When you wear a Citizen, you aren’t just wearing a watch; you are wearing a piece of history engineered for the future.
Why Choose Citizen?
- In-House Manufacturing: Citizen designs and builds its own movements — its Miyota calibers are among the most widely used in the world.
- Built to Last: Citizen engineered its 1960s–70s calibers to be serviced rather than discarded, which is why so many are still keeping good time today.
- Heritage of Firsts: The first light-powered analogue watch (1976, the technology that became Eco-Drive), the first dive watch with an electronic depth sensor, and satellite-synchronised timekeeping.
