Apparently there is a hidden gem within the Apple Watch that Apple hasn't been talking about in the PR literature. The Apple Watch can actually still send/receive texts, activate Siri and more, even when your iPhone is turned off! It does this if it is near your WiFi hotspot, and offers limited functionality. Here's a quote with more of the details,
Apparently the watch can also communicate with an iPhone over Bluetooth or WiFi. This means the two devices can link indefinitely as long as they are under the same WiFi connection, even if they leave Bluetooth range.
...way to leave out one of the coolest features of your new super-watch Apple!