ChargerPay runs when you are charging your phone/tablet and not using it. It plays ads during that time and starts accruing points. Every 100,000 points pays $5 in gift cards (I always prefer Amazon gift cards).
I have reached 10,000 points/day usually (running it on two phones and a tablet). I have gotten paid over $15/month since using it. I use an app with it to keep the screen on all the time as well as diminish the screen brightness to use less power, called Screen On. Without it, usually the screen will time out after 30 minutes and the points stop accruing until I turn the screen back on.