The father of murdered British hostess Lucie Blackman has invented a personal safety service based on mobile phone text messages.

The service launched this week, works on the simple idea of sending a confidential text message to a message facility saying where you are going and with whom.

Along with the text message you set up a set a time delay of between 30 minutes and 24 hours for an alarm to be triggered automatically to alert friends or family in the event that something happens to you. If the message is cancelled within the set time, then no alarm is sent.

The service stores photographs, contact details and the names of friends and relatives, which can be released to the police in the event of the person disappearing.

The service is completely confidential and this is important. Ideally we would want our children to be open and honest about where or what they are doing and whom they are with. But children will always keep some things to themselves.

By being realistic and getting children to use the service we teach them think about the responsibility of situations they get into, and also to consider in advance the consequences.

Students and others overseas can also use the service. Each day you can send a text giving details of where you are going and with who. Delay that text for the time you will be travelling, then cancel it when you arrive safely. If something happens and you can't cancel the text is sent and the alarm is raised.

Each Safetytext message costs 50p on a pay-as-you-go basis or 33p each if paid for by monthly £5 top-up. Full details are on Safetytext