Since the dawn of modern timepieces, mechanical watches have been at odds with magnetism. Magnetic fields can be found in a variety of places, including cell phones, refrigerators, airport security gates, and locks such as those found in handbags or glass cases. Magnetic fields can be so powerful that patients wearing pacemakers should avoid getting too close to them because they can interfere with the proper rhythm of their pacemaker. It's no surprise, then, that it can also de-regulate a mechanical watch!
Magnetism's influence on a mechanical watch.
When a mechanical watch is magnetic, the entire escapement (escape wheel, pallet, and balance staff) is affected because those pieces are usually made of magnetizable steel due to its high stability. Because the escapement regulates the oscillations of the balance wheel, the accuracy of the watch is directly affected, resulting in the watch running either too fast or too slowly, or even stopping abruptly. That is not what we want!
What should I do if my watch is magnetically charged?
If you notice your watch operating oddly, or if you notice a large gap, it is extremely likely that your watch has been magnetized. Bring it to a watchmaker or a professional dealer of mechanical timepieces, since he will have a demagnetizing device. In most cases, simply setting the watch on it will demagnetize it in a few minutes without the need to open the watch.
What about nonmagnetic timepieces?
According to ISO standard 764, a timepiece must be able to withstand a direct magnetic field of 4,800 A/m in order to be considered "anti-magnetic." The mechanism of anti-magnetic timepieces is frequently covered by a shield made of soft iron or mu-metal. The Omega Railmaster, Baltany, and Rolex Milgauss are all well-known anti-magnetic watches!