[dantle]

There isn't a guarantee, but there are incentives for phone/platform providers to avoid spying on you in a battery-powered device. Battery life is still a primary selling point, and these companies are fighting hard to maximize battery life on your device. Turning on the camera is among the most power-hungry tasks, as it activates the image signal processor block of your SoC (which is millions of gates and a high speed transfer interface). It would be difficult to produce a competitive device which spies on its users.