Magnetized Seamaster Pro Chronometer

Checking in from Ft. Walton Beach, FL. I hope I'm on the right part of this forum. If not, let me know and I'll repost accordingly.

I have a Seamaster Pro chronometer which I bought new in 1986. Two tone w/ "James Bond" dial. I recently had it serviced and for a while afterwards it kept perfect time. Suddenly, it started running over 2 minutes fast daily. I checked with a compass and it caused the needle to swing, so I suspected it had become magnetized. I sent it off to be checked/repaired and sure enough, it had become magnetized. The repairman (factory certified) said that it was likely caused by contact with my tablet's speaker.

Is this likely and, if so, will my cell phone, which is like a small tablet, cause this to repeatedly occur? The repair facility couldn't answer this question. Can anyone help me?

I really like this watch, but can't be sending off for repair every month or so.

Thanks very much. Where can I get a suitable demagnetizer. I'm guessing it's a kind of small degaussing device.

Are the apps for the iPhone reliable for detecting and degaussing?

Not really. They have strong magnets in them. The iPhone 12 has big honkin' magnets on the back now for their wireless charging device.

Archer,
Thanks very much for your input. Went to eBay and bought an Etic demagnetizer.

Al, your insights and advice are always appreciated. Are there any major differences in effectiveness between the blue device with a red button anthe the hollow white plastic device? Both are on ebay and both are from China. Thanks, alan

I have the "hollow white plastic device". It does the job. Put your watch in, fire it up, draw it through. Let go of the button once the watch is a good yard/meter away.

@Archer does it matter whether the watch is running? Is there a preferred state?

There was a question earlier about the magnetometers in phones. I think they work quite well. I use an app called 'Physics Toolbox' which gives access to all kinds of sensors inside your phone.