It's fairly obvious that these cameras are never "off". They are simply inactive. When the "power" switch, or rather the physical disable switch, is off, the camera probably does nothing more than occasionally poll that and some other switches, to see if anything happens to it. This can be done in software, on a timer interrupt, or by hardware, where the switch causes an interrupt which wakes up the camera. Even a camera that's "off" will react if you exchange the memory card, for example.
Designs like these cameras typically allow the sequence controller to power down subsystems, to preserve power. But they are never completely off, just disable a number of switches to prevent them being transfered into the active state by mistake.
