Does your smartwatch threaten your mechanical watch?
Founder & CEO, Smartlet - CentraleSupelec engineer - Concours Lepine 2025, Awarded - CES 2026
Contents
Every collector has the same thought exactly once, usually the first time they consider wearing a sensor against a watch that cost them real money: am I about to magnetize the thing I love. It is a fair fear, and it deserves a straight answer rather than a reassuring pat on the head. You are putting an electronic device, full of magnets and circuits, directly against a mechanical movement, and everything in a collector's reflex says keep those two apart. So let me take the fear seriously, then show you why the physics does not share it.
- The mechanism. A magnetized hairspring makes a mechanical watch run fast; that is the real effect of magnetism, and it is usually reversible.
- The threshold. ISO 764 certifies a watch antimagnetic if it resists 4,800 A/m, about 60 gauss, while still keeping time.
- The reality. The magnetic field at a phone's edge measures roughly 2 to 6 gauss, well under that threshold.
- The real threats. Wireless chargers, magnetic bag and bracelet clasps, and speaker magnets, not the wearable you dual-wear.
- The fix. If a watch does get magnetized, a watchmaker demagnetizes it in minutes with no lasting harm.
The fear, and the number
The heart of a mechanical watch is the hairspring, a coil of metal thinner than a human hair that breathes several times a second. When that spring becomes magnetized, its coils cling to each other, the effective length shortens, and the watch starts running fast. That is the whole danger of magnetism in one sentence. Not an explosion, not a dead watch, just a timepiece that gains minutes it should not.
The industry has a number for how much magnetism a watch should shrug off. ISO 764, the antimagnetic standard, certifies a watch if it resists a field of 4,800 amperes per metre, roughly 60 gauss, and still keeps time within about thirty seconds a day afterwards. That is the bar. Now hold it against daily life.
ISO 764 antimagnetic threshold: about 60 gauss. The magnetic field measured at the edge of a phone, where a watch might sit beside it: roughly 2 to 6 gauss. That is a tenfold margin before you reach the level a certified watch is built to ignore. The everyday electronics around your wrist are simply not in the danger range.
Why the wearable underneath is not the threat
A smartwatch does contain magnets, for its charger alignment and sometimes its bands. But the field those produce in normal wear is modest and local, closer to the phone end of the scale than to anything a hairspring fears. Wearing a sensor underneath your watch, held by a non-magnetic pin and adapter, does not bathe the movement in a field it cannot handle.
Two facts make this even calmer. First, many modern movements have stopped caring about magnetism altogether, because silicon hairsprings are inherently non-magnetic; an Omega Master Chronometer is tested to 15,000 gauss and a Rolex Milgauss shrugs off 1,000. Second, the genuine threats to your watch are not the wearable at all. They are the wireless charging pad on your nightstand, the magnetic clasp on a bag or a money clip, the back of a Bluetooth speaker, the magnetic closure on a tablet cover. Those sit far higher on the scale than the watch on your wrist ever will.
So the reflex to separate the two objects is understandable and, on the evidence, unnecessary. If you want the fuller picture of how the two even connect, that lives in the lug hole and the pin, and the accuracy question a collector actually cares about sits in the imprecision premium.
If it ever does happen, it is a five-minute fix
Suppose your watch does pick up magnetism somewhere, from one of the real culprits above. You will notice it running noticeably fast, several seconds or minutes a day. This is not damage. A watchmaker passes it through a demagnetizer, a small device that neutralizes the field in seconds, and the watch returns to normal. Nothing is worn, nothing is broken.
The symptom is almost always the same: a mechanical watch that suddenly gains minutes. If that happens, keep it away from chargers and magnetic clasps and have it demagnetized at your next service. For a piece worth twenty-five thousand and up, have the strap fitted by a watchmaker the first time anyway, and ask them to check magnetism while it is in their hands.
The setup itself is deliberately inert: the watch sits on top facing the sky, the sensor sits underneath against the skin, and a single strap through the central adapter holds them as one object, with no magnet in the connection. The people who compose this deliberately and those adding a first sensor to a serious watch worry about this once, check the physics, and stop worrying.
Keep your watch off the charging pad, not off your other wrist. The brand compatibility index, the Apple Watch compatibility page the collection and the titanium edition cover the rest.
