In response to public outcry via Twitter and personal blogs on Wednesday, the Samaritans have announced an opt-out function for their stalker-friendly app.

Samaritans Radar automatically scans the tweets of anyone the user follows and alerts subscribers to potentially suicidal tweets based on “trigger phrases”. However well-meaning the intention, many Twitter users were quick to point out that there were huge privacy implications, not to mention the creepy effect: “The people you follow won’t know you’ve signed up to it and all alerts will be sent directly to your email address,” according to the Samaritans website.

A recurring theme was that such an over-the-shoulder app could easily be co-opted to harass or stalk someone. “Hey there stalker, no need to read tweets yourself, this handy app will alert you when your target is feeling at their most vulnerable.”

Others said it would force people with mental health issues off the social network.

By the end of day one, the Samaritans said it had received more than 1,500 subscribers and was monitoring around 900,000 Twitter feeds. In its original form, none of those being monitored could opt out. On Wednesday alone the app generated 258 alerts, but with a massive fail rate - only 10 alerts were confirmed as possibly accurate.

On Thursday, the Samaritans issued a statement saying that following “the concerns some Twitter users have raised about certain issues relating to safety and privacy” it would extend its whitelist function to individuals. Originally the whitelist contained only “organisations who regularly tweet using words that the app would normally pick up”.

The organisation says it will do its best to respond within 72 hours to requests to be put on the whitelist, and thus free from monitoring. But some have objected that in order to opt out they must first follow @samaritans on Twitter and send a direct message.

“In developing the app we have rigorously checked the functionality and approach taken and believe that this app does not breach data protection legislation,” said the Samaritans.

However it seems unlikely that they have consulted data protection experts as the app could certainly fall foul of privacy laws.

The app could render the Samaritans a "data processor" with obligations under the current EU ePrivacy Directive. Meanwhile the processing of personal data will almost certainly require “explicit consent” if the new Data Protection Regulation is passed in its current form, something the Samaritans Radar app does not do explicitly. ®