Will a Hero3+ power on automatically when USB power is connected?

I'm hoping to do some long-term time lapse videos using an external battery and was hoping to replicate the basic functionality of the CamDo with a power timer.

Does the presence of power alone trigger the GoPro Hero3+ to turn on, or does a power button have to be pressed once power is connected? If so, how does CamDo do it? I can't seem to find this info when I search.