Reading this it occurs to me I've never had an iOS device lock itself while I'm using it for reading or anything else, nor have I even thought about it as a pos

Reading this it occurs to me I've never had an iOS device lock itself while I'm using it for reading or anything else, nor have I even thought about it as a possibility until this very moment. IMO in that sense iOS already has an equivalent feature. Just don't lock when the user is clearly doing something. Just like how you don't have to shake the mouse to wake your computer while watching a video anymore, most video playback programs/plugins poll the system properly and force it to stay awake. I don't know if you need to go as far as activating the camera to see if you're still there. What if your lock frequency is set to a minute or two? Wouldn't activating the camera every minute have some affect on battery life?