I'm assuming from the blurb that its for emergencies, which makes sense.

But, given the amount of power that needs to be emitted from that watch to make it to the Satellite I assume you need to take it off your wrist first?

No, but it does require you to hold your arm in a particular way. I would be unsurprised if they're factoring in the capacitance and ground plane effect of the "big bag of saltwater" in their antenna design!

It uses the magnetic compass, accelerometer, and GPS to help you aim it at the satellite (south, ~35 degrees above the horizon).