Can locate Apple Watch with serial number
Can I locate watch with my serial number
Apple Watch Series 6
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no, you can't locate anything apple with the serial number
this are your options If your Apple Watch is lost or stolen - Apple Support
however the police if they have a warrant can force carriers to trianglar locate cellular devices if they have the IMEI number, it's at times used to find missing persons, would expect the expense would grossly outweigh the price of any iphone or watch or the likes and doubt they would use it for loss or theft.