I’m confused by the mechanics. How do they know you’re reading unless you have a device that records you reading while you read, so is likely the device you’re

I’m confused by the mechanics. How do they know you’re reading unless you have a device that records you reading while you read, so is likely the device you’re reading on - encouraging people to stare at devices? I actually read on my phone and have since ~2005 and a Palm device. I don’t use e ink or paper much simply because my phone fits in every pocket and is always there. I read constantly at every moment I get a chance to. No other form factor works for that. Even in a suit it fits well in the jacket pocket.