Smartphone Shaker

I commute by train, and when I sit down, there's an older person, maybe around 60, who's constantly shaking their smartphone. They occasionally look at the screen and then keep shaking it. I wonder if they're trying to rack up steps on a pedometer app while sitting, or maybe playing some kind of game. I've seen this a few times before, and today someone next to me was doing it too. Of course, it wasn't the same person. It's not as annoying as restless leg syndrome, but it's still bothersome. It's a bit tiring, like when young people swipe their fingers horizontally really fast for some reason.