How to Demagnetize a Watch

A watch that was keeping perfect time and is now several minutes a day fast has almost certainly been magnetized. It is the most common sudden fault in mechanical watches, it is not damage, and it is fixable in about a minute once you have confirmed it.

The reason it deserves its own page is that people misdiagnose it constantly. A magnetized watch looks broken, feels broken, and gets taken to a watchmaker who charges for a service it did not need — when a $20 plate would have solved it.

What magnetism does to a watch

The timekeeping element of a mechanical watch is the balance wheel and its hairspring: a thin coiled spring that expands and contracts at a fixed rate to release the gear train one step at a time. That hairspring is steel, and steel can be magnetized.

When it is, adjacent coils attract each other and stick together briefly on each oscillation. That effectively shortens the spring, which makes the balance swing faster, which makes the watch gain. The gain is not subtle: minutes a day is normal, and a badly magnetized watch can gain an hour.

Nothing is being damaged while this happens. The steel is magnetized, not deformed, and removing the magnetism restores the original rate exactly.

Why it happens so easily now

Modern homes are full of strong magnets that did not exist when watch cases were designed. Laptop and tablet lids use them to latch. Speakers contain them. Magnetic phone mounts, phone cases, handbag clasps, cabinet catches and induction hobs all contain them.

ISO 764 defines a magnetic-resistant watch as one that survives a direct-current field of 4,800 A/m and still keeps its pre-test rate to within ±30 seconds a day. That is a specification a watch has to be built to pass, and most affordable automatics make no claim to it at all.

Confirming it: the compass test

Do this before buying anything. It takes thirty seconds and costs nothing.

1. Lay a compass flat on a table, well away from steel furniture, speakers and your phone. Let the needle settle.
2. Bring the watch slowly toward it from a few inches away, then rotate the watch as you go.
3. If the needle deflects and follows the watch, it is magnetized. If the needle does not move at all, magnetism is not your problem and you should stop here.

A phone compass app works, though less reliably — the sensor is inside a device that also contains magnets, so a physical compass gives a cleaner answer.

One extra step worth taking: remove the strap or bracelet and test the watch head on its own. Milanese mesh bracelets with magnetic clasps and some aftermarket straps are themselves magnetized, and demagnetizing the watch while leaving a magnetized bracelet attached simply re-magnetizes it.

The fix

Using a demagnetizer

A watch demagnetizer is a small mains-powered plate. It works by applying an alternating magnetic field that reverses direction rapidly, which randomizes the alignment of the magnetic domains in the steel — the same alignment a static magnet imposed in the first place.

The technique matters more than the device:

1. Place the watch on or beside the plate.
2. Press and hold the button so the field is active.
3. Withdraw the watch slowly, to a foot or more away, while still holding the button.
4. Only then release the button.

Withdrawing slowly through a decaying field is what randomizes the domains. Releasing the button with the watch still sitting on the plate can leave it magnetized at whatever phase the field stopped at — which is why people occasionally report that a demagnetizer “made it worse.”

Repeat the compass test. If the needle still moves, run another pass with the watch in a different orientation. Two or three passes clears essentially every domestic case.

Taking it to a watchmaker

Any watchmaker has a demagnetizer and this is normally a walk-in, few-minutes, low-or-no-cost job. If you own one watch and it has been magnetized once, this is the rational answer. If you own several automatics, or you work near magnets, owning a plate pays for itself quickly.

Verifying the fix

Demagnetizing is instant, but proving it worked takes a day. Set the watch against a network clock, wear it normally, and compare after 24 hours.

The result should fall back inside the maker’s stated window. Seiko publishes roughly −35 to +45 seconds a day for its common 4R calibers — a wide window, and an honest one for a workhorse movement. Even a COSC-certified chronometer, tested over about fifteen days in five positions and three temperatures, only guarantees an average of −4 to +6 seconds a day. Our accuracy guide covers how to measure properly rather than by impression.

If the watch is still gaining minutes after two clean demagnetizing passes and a clear compass test, magnetism was not the cause and it is time for a watchmaker — our service cost guide covers what to expect.

Keeping it from happening again

You cannot magnet-proof an ordinary watch, but you can change three habits.

• Do not rest a watch on a laptop, tablet or speaker. These are the three commonest sources by a distance, and a bedside habit of putting the watch on a closed laptop is how most watches get magnetized.
• Keep watches away from magnetic phone mounts and cases. Modern phone accessories contain genuinely strong magnets.
• Store watches in a padded box, not a drawer of gadgets. Our guide to storing automatic watches covers the other two storage hazards, which are moisture and watches knocking together.