An app designed by the Samaritans has been criticised over privacy issues.
Samaritans Radar works on the basis that if someone signs up a friend or family member their twitter account will be monitored.
The service look for key words that indicate the friend is in trouble and notifies the user without the tweeter knowing.
By Friday 3000 people had signed up.
Campaigners and data protection experts have slammed the app over privacy issues and say that it could encourage on-line trolls to target the vulnerable.
An on-line petition is urging the charity to withdraw the app.
The Samaritans says it is talking the concerns very seriously.
