watch demagnetizer test

My newly tuned up Speedmaster suddenly gained half a minute overnight. So I checked it and found the timegrapher showed more than +20 seconds a day.
A quick google said the likely cause was magnetism and a compass did show it was slightly magnetized.

So I bought two cheap watch demagnetizers on Amazon. A blue "Tui Ci Qi" unit for about US$13 and a white "HUAXING" unit like a mini MRI machine for about US$20.

I put both of these devices on a power meter, and found the blue one used about 7.6W and the while one about 23.3W. And then I played with both, magnetizing and demagnetizing a small screwdriver. IMO opinion the white unit worked better, but it could be the technique.

For the blue unit, most recommend putting the watch on the pad, turning the unit on and then slowly lifting the unit up and away from the pad for more than 24" (60cm) before turning the unity off. But some recommend rubbing the unit back and forth and around on the pad. I tried both with my magnetized screwdriver with variable results.

For the white unit, most recommend putting the unit in the unit's hole, turning the unit on and then pulling the watch out and away from the unit for more than 24" (60cm) before turning the unit off. However, some people recommend passing the watch completely through the unit from one side to the other.

For either unit, multiple passes could be used to possibly improve the results. I found the white unit consistently demagnetized my screwdriver in one pass.

I made a video showing a demonstration of the white unit:

I did disassemble both units, and both are VERY crudely made. I highly recommend only plugging these in when using them and unplugging them when done!

Interior photos for those that are curious.


Oh, after a pass through the white demagnetizer the performance of my Speedmaster is restored. ;-)

Hmm, I made a variety of typos above and the forum doesn't seem to allow editing after a couple minutes. Here is some of the key text fixed:

For the blue unit, most recommend putting the watch/tool on the pad, turning the unit on and then slowly lifting the watch/tool up and away from the pad for more than 24" (60cm) before turning the unit off. But some recommend rubbing the watch/tool back and forth and around on the pad. I tried both with my magnetized screwdriver with variable results.

For the white unit, most recommend putting the watch/tool in the unit's hole, turning the unit on and then pulling the watch/tool out and away from the unit for more than 24" (60cm) before turning the unit off. However, some people recommend passing the watch completely through the unit from one side to the other.

Also, that the manufacturers note these heat up and recommend only using them for a very short time before letting them cool off. The white unit says to use it for 1 minute maximum. I did disassemble both units, and both are VERY crudely made. I highly recommend only plugging these in when using them and unplugging them when done!

The watch in this case is my Speedmaster Automatic Reduced 3539.50.00. I don't think it has any shielding with the snap-on back. It was clearly magnetized, as evidenced by compass and phone app magnetometer. Problem solved with a couple passes through the demagnetizer.

Thanks, interesting post.

I think @Watch my Whisky should have commented " DM me for putting units in other units hole". I miss those posts.

The white one is the better (and more expensive) of the two. One thing to watch out for is overheating if left on too long.

A compass is not the best tool for detecting magnetism as it will show you the watch cases effect on the earth's magnetic field. From that standpoint, any chunk of ferrous metal is magnetized. The compass needs to be small and very close to the balance and hairspring, closer than you will get with the watch cased. You need to see the compass respond to the movement of the balance, which isn't easy.

Your technique is correct but you don't necessarily have to do it slowly, 60 Hz is pretty fast. You just have to separate them by a foot or so.

I have both but only use the blue box for demagnetizing disassembled parts before the sheep dip.