Like your iPhone, your Apple Watch has a Wi-Fi antenna inside of it, which allows it to connect directly to Wi-Fi networks (or via your iPhone) rather than always using your cellular data.
Where the two devices differ is in how they can connect: The Apple Watch doesn't have an Auto-Join Wi-Fi screen, or a place to select networks, nor does it have an option to dictate or Scribble in passwords. In short: Your Apple Watch can't connect to Wi-Fi unless your iPhone has first connected to it.
Essentially, when your iPhone connects to a Wi-Fi hotspot and enters in the password while you're also connected to Apple Watch, your iPhone syncs that information over to your Watch.
Apple Watch can then access that information and connect to a network — even if you visit that location in the future with only your watch. That way, you can use all of your Apple Watch's online capabilities in Wi-Fi areas (like Messages, Maps, and any third-party apps) whether you have a GPS + Cellular model or a Series 0 Apple Watch.
Sounds easy enough, right? Keep in mind: There are still a few limitations.
Where Wi-Fi fails on Apple Watch
Because Apple Watch doesn't have the Wi-Fi chops of its paired sibling, it struggles with a few areas, as outlined in a Support article on Apple.com. Namely:
- You won't be able to connect to a new Wi-Fi network unless your iPhone is present and can connect to it.
- Your iPhone needs to be paired with Apple Watch when it connects to the network — it doesn't work over iCloud Keychain
- Apple Watch can only use 802.11b/g/n 2.4GHz networks, not 5GHz networks.
- Apple Watch shouldn't connect to any public network that has an interstitial captive, like a hotel login, Google Starbucks terms and conditions acceptance, or other subscription information
If all else fails and you have cellular service enabled, your Apple Watch should just fall back to using LTE service.
How to tell if your Apple Watch is connected to Wi-Fi or cellular networks
When your Apple Watch connects to a Wi-Fi network instead of your iPhone or cellular, you'll see a different symbol when you swipe up on Control Center from the watch face: A green "Connected" cloud icon, or (Cellular model only) blue Wi-Fi bars.
Any other questions about Apple Watch and Wi-Fi?
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Updated November 2017: Updated for watchOS 4.