Smartphone addiction has become so endemic these days, that having an obsession with your mobile barely raises an eyebrow anymore. But if you’re still busy checking your cellphone while you're with your children, you’re not just missing out on their childhoods, you may also be putting them in danger.

A father from Shanghai learned this lesson the hard way, after his children went missing in a subway station while he got lost in a dangerously addictive mobile game.

The father was so absorbed in scanning the Chinese character “fu” (福, meaning “happiness” in English) through his Alipay app that he boarded a subway train, leaving his three kids alone on the platform. Luckily a member of staff soon noticed the kids wandering about in the station, and helped them reunite with their negligent dad.

So what is this game, and why are people obsessed with it? It is a new augmented reality (AR) feature introduced by Alipay for this year's Spring Festival, building on the craze in recent years for digital "hongbao" (红包, red envelopes stuffed with cash handed out for good fortune to mark Chinese New Year). This traditional custom has been picked up by Internet giants competing to promote their mobile payment services, by offering mystery gifts and bonuses to lucky users.

Alipay came up with the challenge of collecting "fu" cards last year. Users of the payment app were entered into a 215-million-yuan prize draw on lunar New Year Eve, as long as they could acquire five types of “fu” cards. The cards were obtained by inviting friends to shake their phones while watching the CCTV Spring Festival Gala, an annual broadcast watched by hundreds of millions of people nationwide.

This year however, the “fu” card campaign has gone real. Thanks to AR technology, the game can be played anywhere, anytime. Players can collect the cards by scanning anything with the Chinese character "fu" on it, no matter if it’s a poster attached to your door, or even a crudely drawn "fu" written on your hand.

Since its launch, people have gone crazy about scanning “fu,” with the game really pushing card hunters to use their imaginations. Some have found luck in unlikely places, such as finding the character inscribed on tombstones.

Are you ready for this year's hongbao battle? If you are, stay safe and watch your kids! Feel free to share your experience with us.