Ms Blackman's remains were found seven months after she vanished

Tim Blackman's 21-year-old daughter Lucie was drugged, raped and murdered.

Her father, 51, of the Isle of Wight, said the scheme let people send a delayed message if they felt unsafe.

The text message is stored for up to 24 hours, which the user cancels if they arrive safely. If they do not arrive, the message is sent to raise the alarm.

Lucie Blackman was working as a nightclub hostess in the Roppongi district of Tokyo when she vanished in July 2000.

Trial under way

The former flight attendant, from Sevenoaks, had told a room-mate she was going to the seaside, but did not say who with. It was the last time anyone heard from her.

Her dismembered body was found in February 2001 after a seven-month search.

Japanese property developer Joji Obara, 52, went on trial last year accused of abduction, rape and disposal of the body, as well as attacks on other women - he denies all charges.

Lucie's father said: "Here is a device that people should use as a way to make sure that if something happened to them, somebody would know where to start looking.

"Don't think 'oh well, it won't happen to me', because it can happen to you."

He said the text scheme would have allowed his daughter to be found in seven hours rather than seven months.