How to find the serial number or IMEI for your Apple Watch - Apple Support
Apple(アップル) / スマートウォッチ/Apple Watch Series 3 42mm GPSモデル/デジタル/ラバー/BLK/W | 中古品の販売・通販ならセカンドストリート
How to Find and Check Apple Watch Serial Number
My Development Apple Watch Series 1! This device doesn't run WatchOS, but an internal Apple testing operating system (called “SwitchBoard”) and it's serial number is invalid! : r/AppleWatch
How to find out what series my Apple Watch is?
How To Check Your Apple Watch Serial Number In The Correct Way
Apple Watch Series 3 Serial Number Lookup - AppleSN.info