Sure they could, but it's unlikely. The device would have to permanently have the mic enabled and be listening out 24x7 just in case. Battery life would be terrible.
Makes sense to enable it when on power as the device may well be in a car.
It doesn't kill the battery on android. I use the Moto voice on my Moto X without it killing the battery.
It's working on the Apple Watch. And the Watch has a very very very tiny battery.
It doesn't kill the battery on android. I use the Moto voice on my Moto X without it killing the battery.
The Watch face must be on for 'Hey Siri' to work.