Demagnetising
Demagnetising is the process of clearing the magnetic field from the magnetised parts of a mechanical watch. When a watch suddenly begins running very fast, magnetism is often to blame. A small tool called a demagnetiser puts it right in seconds, cheaply.
At a glance
- Typical symptom
- The watch suddenly gains minutes a day
- Tool needed
- A demagnetiser, usually a small device costing roughly £10 to £20
- Time required
- A few seconds, without opening the case
At the heart of a mechanical watch is a fine steel hairspring that breathes in and out hundreds of times a minute. If that spring becomes magnetised, its coils cling together, its effective length shortens, and the watch can gain minutes a day. The fix is to undo the magnetic field, not to repair anything.
Why magnetism happens
Everyday life is full of fields strong enough to magnetise a watch, and most are harmless:
- Speaker and earbud magnets: laptops, phone cases, Bluetooth speakers
- Magnetic closures: bags, tablet covers, fridge doors
- Some medical equipment and power tools
This is why a sudden change in timekeeping is not always a fault. Antimagnetic watches resist the effect better, though none are wholly immune.
How the process works
A demagnetiser generates an alternating magnetic field. You hold the watch inside the field, then draw it slowly away; as the field fades, the residual magnetism in the parts settles towards zero. It takes seconds and is done without opening the case.
If the timekeeping wandered before you reached for the tool, that is a normal accuracy deviation. For everyday picks worth looking after, see our guide to the best Japanese watches.
Examples
If your mechanical watch kept good time yesterday but is gaining four or five minutes a day today, suspect magnetism first. Pass it through a demagnetiser for a few seconds and measure again; in most cases the rate returns to normal.
Leaving a watch overnight on a laptop speaker and finding it fast in the morning is a textbook magnetism case, and reversing it takes seconds rather than minutes.
Comparison
The same symptom, a sudden speed-up, can point to two very different situations. Telling them apart decides which fix you need.
| Option A | Option B | Notes |
|---|---|---|
| Magnetism | Mechanical fault or service due | Magnetism is undone with a demagnetiser in seconds at near-zero cost; a fault needs a watchmaker to open and service the calibre. |
| Demagnetising | Sending it in for service | Try demagnetising first. If the rate does not settle, the problem is not magnetic and a genuine service is warranted. |
Related terms
Frequently asked questions
Can I demagnetise a watch at home myself?
Yes. An inexpensive demagnetiser does the job in seconds without opening the case. You hold the watch in the field, switch it on, and draw it slowly away while it is still running. With quartz watches it is different: magnetism usually only stops or disturbs them temporarily and rarely calls for demagnetising, and a standard demagnetiser can damage the stepper motor's permanent magnet, so a quartz piece is best left to a watchmaker.
Can I demagnetise a watch at home myself?
Yes. An inexpensive demagnetiser does the job in seconds without opening the case. You hold the watch in the field, switch it on, and draw it slowly away while it is still running. It is safe for quartz watches too, though they rarely need it.
Does an antimagnetic watch never need demagnetising?
Less often, but never is too strong a word. Antimagnetic watches protect up to a rated field strength; expose one to a much stronger field and it can still magnetise. The remedy is the same: a quick pass with a demagnetiser.