If your automatic watch is suddenly running fast by several minutes a day, the most likely cause is magnetism: its hairspring has become magnetised. You can check in thirty seconds with your phone's compass, and a watchmaker can demagnetise it in a few seconds. Nothing is permanently damaged.
What magnetism does to a movement
The heart of a mechanical watch is the hairspring: an extremely fine coiled spring that oscillates with the balance wheel and sets the watch's rate.
When the hairspring becomes magnetised, its coils partly stick to one another. The spring effectively becomes shorter, therefore stiffer, therefore faster. The watch gains time — sometimes a few seconds, sometimes several minutes a day.
That is the signature of magnetism: a magnetised watch almost always runs fast, not slow. If yours is losing time, look elsewhere.
Where magnetisation comes from
The sources are ordinary and everyday. Magnetic clasps on bags and tablet cases. Speakers, even small ones. Wireless chargers. Magnetic phone mounts in cars. Fitness band clasps.
None of these objects is dangerous in passing. The problem comes from prolonged proximity: a watch placed every night next to a wireless charger builds up exposure.
How to tell if your watch is magnetised
Two simple methods.
The compass. Open the compass app on your phone, lay the phone on a table and slowly bring the watch close to it. If the needle clearly deflects, the watch is magnetised. It is not laboratory-grade precision, but it detects the serious cases.
Its behaviour. A watch that suddenly gains more than two minutes a day, after months of keeping steady time, is magnetised until proven otherwise.
How to demagnetise a watch
This is one of the rare watch faults that is completely reversible and inexpensive. A watchmaker demagnetises a watch in a few seconds with a dedicated device, often for a nominal charge, sometimes free of charge.
Home demagnetisers also exist for around €20. They work, but used incorrectly they can make things worse — if you are not sure, leave it to a professional.
Magnetisation never permanently damages a movement. The watch returns to its original accuracy.
Watches that resist magnetism
Some pieces are designed to be anti-magnetic. Omega Master Chronometers resist 15,000 gauss thanks to non-magnetic components. Modern Rolex watches use a Parachrom hairspring. Historic IWC Ingenieur models had an internal Faraday cage.
If you own one of these, the question is largely theoretical. For everything else — which is most watches in circulation — it applies.
What about a watch winder?
A watch winder is a motorised device, switched on permanently, with your watch sitting on it. So the question is a fair one.
A properly designed, shielded motor is not a problem. Models with anti-magnetic protection also isolate the calibre from external fields — from the speaker, computer or charger sitting on the same desk.
On a device meant to stay switched on for years next to your watch, this is a feature worth checking before you buy. Browse our watch winders, and for the right rotation settings, see watch winder settings by calibre. If you are worried about wear rather than magnetism, read are watch winders bad for watches?
In short
A watch that suddenly runs fast is magnetised nine times out of ten. Checking takes thirty seconds with a compass, the fix a few seconds at a watchmaker's, and nothing is permanently damaged.
Prevention fits in one sentence: keep your watch away from speakers, wireless chargers and magnetic clasps.