Serial numbers for all Apple Watches may be found:
- On the Apple Watch, in the Settings app > General > About > Under Serial Number
- On the paired iPhone, in the Apple Watch app > Click the My Watch app > General > About > Under Serial Number
- Original Purchase Receipt
- Apple Store Repair Receipt or AASP Repair Receipt
Apple Watch Series 0 (1st Generation)

The serial number is engraved on the back of the Apple Watch.
All Apple Watches

The serial numbers are on the inside of the lower band slot.