So you think your Apple Watch with a passcode is safe from thieves. As the folks at iDownloadBlog have shown, it is pretty easy to bypass the passcode and pair a stolen Apple Watch with a new phone using a different Apple ID. They managed to reset an Apple Watch which was paired with an iPhone 6 Plus and pair it with an iPhone 5s which is signed in using a different Apple ID.
The Apple Watch does not have the ability to established its own dedicated WiFi or cellular connection at this point. But there are still things Apple can do to protect Apple Watch owners. In the meantime, you may want to be more careful not to lose your watch.