Students are back in classrooms and parents can finally have a brief respite from worrying about their children's excessive screen use — or, at least, worrying it is all their fault. This angst peaks each year in the summer holidays, those long, sunny weeks illuminated in large part by the blueish light from children's smartphones, tablets and laptops. The beep and ping of devices triggers complicated emotions. In many homes, parents simultaneously castigate their offspring's use of tech and are relieved by it: like some goblin babysitter, it squats in the corner of family life, whispering powerfully, turning children silent and glassy-eyed.

The erratically applied adult phrases 'That's enough screen time!' and 'Give me that iPad!' ring hopelessly around family homes, interspersed with squeals of refusal. Cannier parents have worked out that if they cannot contain the addiction they can manipulate it to their advantage: the threat of sudden iPad withdrawal is a behavioural corrective that trumps the useless 'naughty step' every time.