Yes—the Sinn Dual Strap System was a real accessory for wearing a mechanical Sinn watch and an Apple Watch on the same wrist. Contemporary 2016 reports specify Sinn watches with 22 mm lugs and Apple Watch models in the 38 mm and 42 mm case families. The reported price was €175, or €100 when ordered with a new Sinn watch.
The original system now appears to be a historical product rather than a clearly current Sinn accessory. Do not confuse it with Sinn’s current DuoFlex diving strap, which is a different product and is not documented as Apple Watch-compatible.
What the Sinn Dual Strap System was
This was not simply two ordinary bands worn side by side. It was a combined strap arrangement using shortened strap sections for the mechanical watch, Apple Watch-specific connectors, and a bridge that held both watches together on one wrist. Contemporary descriptions also list replacement spring bars, a strap-changing tool and a storage case.
The concept let the Sinn remain the visible mechanical watch while the Apple Watch supplied notifications, calls, timers, activity tracking and other connected features. A French report described it as two small watch straps attached to one another, with one watch mounted at each position: WatchGeneration’s 2016 description.
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Compatibility: the original specification is narrow
| Component | Documented compatibility |
|---|---|
| Sinn watch | Sinn models using 22 mm lug widths |
| Apple Watch | 38 mm and 42 mm case-size families |
| Later Apple Watch sizes | Not established; confirm with the seller before buying |
| Current Sinn DuoFlex | Different diving strap system for selected U-series watches |
The 38 mm and 42 mm references come from the original-era documentation, not a promise of compatibility with later 40 mm, 41 mm, 45 mm, 49 mm or newer Apple Watch size groupings. A 20 mm Sinn, such as a Sinn 103, is not automatically compatible with a system designed for 22 mm lugs.
Read the historical specifications in MacTechNews’ report before assessing a used kit.
How the combined setup works
What was supplied
- Two shortened strap halves with Apple Watch connectors.
- Two shortened strap halves for the Sinn watch.
- A bridge strap for coupling the watches, with the reported option to wear them separately.
- Replacement spring bars and a strap-changing tool.
- A case or storage pouch.
Positioning on the wrist
Most users would place the Sinn on the outside of the wrist for normal watch reading and the Apple Watch on the inside. That can keep the mechanical watch visually prominent, but the Apple Watch becomes harder to glance at and operate. The correct orientation depends on whether the priority is discreet notifications, health sensing or easy controls.
Apple Watch function is a fit question
Mounting the Apple Watch does not itself guarantee normal sensor performance. Reliable heart-rate, workout, sleep or fall-detection readings depend on the rear sensors remaining against the skin, with a secure but comfortable fit. The crown and side button also need to remain accessible, and the case must not obstruct charging hardware.
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The original Sinn reports do not provide laboratory results for sensor accuracy, sleep tracking or fall detection. Smartlet recommends inner-wrist placement with the sensors against the skin for its own adapter, but that is a vendor recommendation rather than independent validation: Smartlet’s setup guide.
Comfort and daily trade-offs
Two cases inevitably weigh more and occupy more wrist space than either watch alone. Pressure can develop at case backs, lugs or the connecting hardware, especially when the band is tightened enough for Apple Watch sensors. A large Sinn diver or chronograph can make the arrangement especially bulky.
- Small wrists may not provide enough flat surface for both watches.
- Sleeves, cuffs and gloves can catch on the combined thickness.
- The watches may shift or contact each other while the wrist moves.
- The Apple Watch can be awkward to consult on the underside of the wrist.
- Frequent charging may require removing the Apple Watch from the arrangement.
These are design trade-offs, not independently tested comfort results. Wrist circumference, case thickness, strap material and placement will determine whether the arrangement is tolerable.
Price and present-day availability
Contemporary coverage reported €175 for the standalone system and a €100 surcharge when it was ordered with a new Sinn watch. Those are 2016 historical prices, not current retail quotes.
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The original Apple Watch-compatible system is not clearly listed in Sinn’s current online accessory catalog. Sinn’s current catalogue is available at Sinn’s 2025/2026 catalogue, while old reseller references such as this Sinn 836 listing do not prove ongoing manufacture. Treat the Dual Strap System as old stock or second-hand unless Sinn or an authorised dealer confirms availability.
Do not mistake it for Sinn DuoFlex
Sinn’s current black DuoFlex system is a diving strap for the U1, U2 and UX series. Sinn lists 22 mm lug and buckle widths, silicone strap parts, a bead-blasted stainless-steel folding clasp, quick length adjustment, case adapters and TEGIMENT-treated components. The German store lists it at €425 including German VAT.
DuoFlex is not documented as an Apple Watch carrier. Its product page is Sinn’s black DuoFlex diving strap page. Buying it expecting the historical dual-watch function would be a compatibility mistake.
Buying an original system second-hand
Verify the watch and Apple Watch dimensions
Confirm the Sinn’s actual lug width rather than relying on the model name. Confirm the Apple Watch case and connector family; “Apple Watch compatible” is not sufficient for a later-size watch.
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- Compatibility: Fit for GA-110/100/120/150/200/300/400, GD-100/110/120/G-8900/DW-5600, GW-M5610/DW-6900/G-5600, GW-6900/DW-9052/GLS-8900.
- 16mm to 22mm: The size of the protrusion is 16mm. Easily convert a 16mm port to a 22mm band, making your watch compatible with a wider variety of stylish 22mm straps.
- Package includes: 4 black adapters + 12 spring ears + 2 tools. Note: Watch and Band are Not Included!
- How to Check Compatibility: 1. Locate your model number (e.g., GA-110) on the backplate of your watch. 2. Measure the lug width (L) – the internal distance between the strap arms. If it measures 16mm, this case is a suitable match.
- Material: These adapters are crafted from tough ABS material, offering a lightweight yet durable solution. Each set includes spring pins and installation tools for quick and easy setup. Ideal for situations where your strap is still intact but the connector needs replacing.
Request a complete-parts photograph
- Both Sinn-side strap halves.
- Both Apple Watch-side strap halves or connectors.
- The bridge strap.
- Correct spring bars.
- The strap tool, if included.
- The storage case, if completeness matters.
Inspect age-related wear
Look for stretched, cracked, hardened or chemically degraded rubber, bent connectors and damaged spring-bar holes. Two watches also create more leverage on the strap and spring bars. Metal hardware can scratch lugs or cases during fitting; use a competent watchmaker if you are not experienced with spring bars. No adapter should be assumed to preserve water resistance unless the manufacturer confirms it for the exact watch and installation.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Modern alternatives
Smartlet
Smartlet’s 2026 guide describes an adapter in which one continuous strap passes through a holder, the mechanical watch attaches at its normal lugs and the Apple Watch slides into its connector. Smartlet specifically describes support for the 20 mm-lug Sinn 103 and current Apple Watch connector families. Its published versions and prices in that guide are Classic €299, Shadow €399 and Titanium €549.
Those compatibility, pricing and positioning statements are Smartlet’s own claims. The available information does not independently establish comfort, durability, sensor accuracy or water-resistance performance. Verify the exact Sinn case geometry and Apple Watch size before ordering. Smartlet’s vendor site is smartlet.io.
Two wrists
Wearing one watch on each wrist avoids adapter compatibility, case-rubbing and sensor-position problems. It is generally easier to operate the Apple Watch and leaves both watches visible, although some people find the look impractical or conspicuous.
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A normal Sinn strap or Apple Watch alone
A conventional Sinn strap is the cleanest choice when mechanical-watch comfort matters most; Sinn lists model-specific options such as its blue integrated silicone strap. Apple Watch alone remains the least compromised option for workouts, sleep and health monitoring.
Who should consider dual-wearing?
- Collectors: The original Sinn accessory is appealing if you specifically want a period-correct, unusual Sinn solution and can verify a complete 22 mm kit.
- Notification-focused users: A combined setup may work if the Apple Watch is mainly a discreet utility device and sensor demands are modest.
- Fitness and sleep users: Check sensor contact and charging routines carefully; the underside-wrist position may be inconvenient.
- Owners of large divers or small wrists: Expect the highest risk of bulk, pressure and cuff interference.
- Formal or protective-clothing wearers: A conventional strap or two-wrist solution is usually less obstructive.
Frequently Asked Questions
Is the Sinn Dual Strap System still sold new?
Its current official availability is not established. It is not clearly listed in Sinn’s current online accessory catalog, so buyers should treat examples as old stock or second-hand unless an authorised dealer confirms otherwise.
Will it fit a modern Apple Watch?
Do not assume so. The documented original specification names 38 mm and 42 mm Apple Watch models; later case sizes and connector groupings require separate confirmation.
Is Sinn DuoFlex the replacement for the Dual Strap System?
No. DuoFlex is a current diving strap for selected Sinn U-series watches, not a documented Apple Watch dual-wear adapter.
The Bottom Line
The Sinn Dual Strap System was a clever but niche 2016 accessory, not a universally compatible Apple Watch band. If you find one, verify the 22 mm Sinn fit, the 38/42 mm Apple Watch connector, every included part and the strap’s condition. For newer Apple Watch sizes or different lug widths, a clearly identified third-party adapter such as Smartlet—or two separate wrists—is the more realistic path.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
