My Apple Watch is setting off store security alarms

NFC = Near Field Communication. It's what lets you use Apple Pay from your watch (or iPhone). If you live in the U.S. and have a relatively current passport, your passport has an RFID (radio frequency identification) chip in it. If you get a pet from the ASPCA, they are "chipped" with an RFID device about the size of a grain of rice that can be scanned, giving vets or rescue organizations access to information on how to contact you. Store theft control systems often rely on RFID tags on merchandise which will trigger an alarm if you try to leave. All of these things have to be fairly close to the reader (hence "Near field") to be detected.

Try walking through the very center of the entry to the stores rather than near the sides where the readers often are.

Store security measures vary. For example:

https://en.wikipedia.org/wiki/Electronic_article_surveillance

Over the years, various Apple devices have been reported by users as having triggered store alarms.

It may help to place your watch into Airplane Mode when entering or exiting stores where you have learned, by experience, that this issue may arise:

https://help.apple.com/watch/#/apd6e1809c9e

Otherwise, be sure to ask the security personnel to let the store manager know that Apple Watch is triggering false alarms. This may help lead them to make whatever changes may be necessary.

Did you ask at those stores if they've seen this issue with other Apple watches? I'm guessing they have RFID detectors of some sort and they're picking up on the watch. As it doesn't appear to be a particularly common problem, I suspect there's something about those particular anti-theft systems. I don't know enough about to them to know if they are in any way adjustable but it might be something you could suggest.

There is no way to turn off the NFC in the Apple Watch that I know of.

I've also seen the key fobs for some automobiles that are used to lock/unlock the doors set these things off. Sometimes it has to do with how high off the floor they are. As others have indicated, all types of these security systems exist, and different interference can cause different things. Some have indicated that Bluetooth has an affect. It may be in the best interest of the retail store to have their devices calibrated by their supplier/service provider.

You're welcome!