A father was so fed up with his teenage son ignoring his messages that he created an app - to force him to text back.
Nick Herbert reached the end of his tether because 13-year-old Ben kept screening his calls - so he created a mobile app that locks phones until they respond.
The 45-year-old built the ReplyASAP messaging app which takes over the recipient's phone screen and sounds an alarm - and doesn't stop until it is answered.
Parents are then told if their kids have seen their message and if the troublesome teen's phone is turned off then a message pending sign will show on the sender's phone.
Now Nick, of West Wickham, south east London, is selling his creation to help stressed out parents across the country keep track of their children.
He said: "My son started at Langley Park School for Boys a couple of years ago and has a smartphone.
"I thought this would make getting hold of him easier, but it doesn't at all.
"In fact, he is always playing games and has the phone on silent. It drives me crazy.
"I'm hoping the app will make our relationship better.
"It will alleviate the stress when I can't get hold of him as I will know that he has seen my message."
But Nick has one problem left to overcome, his app only works with Android and his son has an iOS phone and is keen to get his app working on iPhone devices as soon as possible.
Parents might be pleased but Nick acknowledged teens might be wary of the intrusive invention.
He added: "As they are teenagers I realise they aren't going to be massively keen. My son hasn't really said anything negative about the app. It is all about him understanding why it's there.
"If I have something important to say I will send an urgent message. Hopefully It will make things a bit easier.
"Will it be the bane of his life? Maybe, I'm not going to be using it all the time to speak to him. It is supposed to be a failsafe."
The process of building the app has taken eight months and has been complicated and expensive, but Nick reckons it'll take off.
He hasn't always been sure that other parents will be as happy with ReplyAsap Messaging App as he is and must see if his idea will take off.
The app costs 99p to snoop on one person, £2.49 to track four people, £6.99 for ten people and £12.99 for platinum, which connects with 20 numbers.
All users get one free connection when they download the app and will be able to connect to one child for free, before having to pay.
Nick said: "I was speaking to some people and saying what the apps does and why I built it.
"A person said: 'why don't you just phone him because that I would do.
"I thought 'maybe it is just my son who has his phone on silent the whole time.'
"Do everybody else's' kids keep their phones on?
"But after speaking to other parents I think there is an issue that the app would address. It seems to be something that does resonate."