Is my laptop secretly watching me?

This is not an SOS but possibly a hidden feature observation I’ve made. Please correct me if I’m wrong because a brief search on the web suggests I’m the only one to have noticed this. After putting my iMac into sleep mode and I return to my home office after a long period, I’m convinced that my iMac’s camera detects my movement and wakes it up, anticipating that I’m about to log in. It doesn’t turn on the screen but gets the login screen ready for when I hit a key or click the mouse. I’m only suspecting this because I have external drives that start spinning when I enter the room. I’m not quite sure if my iMac hard drive starts too due to the noise from them but I think it must do. I’ve always thought ‘how clever’ though sometimes I do think it’s a bit ‘Big Brother’ spooky! Moelwyn Hopkins This does happen, but it isn’t using the camera. The camera is connected to the green LED through a hardware interlock, so it can’t be active without also turning on the LED. Instead, OS X uses the ambient light sensor to detect movement in front of the screen. This should only stop the Mac from going to sleep; it won’t make it ‘ get ready’ if it’s already asleep. But external drives might be triggered to wake up that way.