Bluetooth Low Energy must be really low power: the design of
WKInterfaceObject means it’s going to be on a lot. Every
interaction with the watch has the potential to move actions and
data between your pocket and wrist using the radio.
But more importantly, this API design gives Apple a simple way to
put a cap on power consumption. We saw this approach in the early
days of the iPhone and that worked out pretty well, didn’t it?
One final thought about the API design: your code never runs on