Andrew Leavitt, writing for 17 Orbits:

Starting in 2010 Mobile Me enabled you to hunt down your missing iPhone (or iPad) with the Find My iPhone app. In 2011 OSX Lion added ‘Find My Mac’ to the mix. Beginning this week watchOs 3 enables iCloud to locate your misplaced Apple Watch.

And:

Until now real-time geolocation was only possible if your missing Apple Watch and iPhone were in Bluetooth range or on the same WiFi network. Since the watch does not have its own cellular signal that would seem to limit location tracking to within 10 meters or your home WiFi. Once out of range, however, iCloud now kicks in and reports the watch’s present location by GPS or WiFi triangulation. If the watch is turned off the last known location is reported. Accuracy is enhanced because the Apple Watch can still connect to previously known WiFi on its own (even when phone is physically far away).

Read the post and give it a try. You can track your Apple Watch (along with all your other Apple devices) and play a never ending (until you tap Dismiss) sound on your Apple Watch. Great for finding it when it slid between the couch cushions or when you are challenged, unwillingly, to a morning game of find your gear.