The "Citizen" app is supposed to give New Yorkers a timely warning about crimes being committed in their neighborhoods. But, while the aim is to encourage civic awareness, it could make life more difficult for police. It doesn't sound such a bad idea. Those with the Citizen app will be alerted by a push notification whenever a crime is committed in their neighborhood - or if they get too close to the scene.

A video from the company behind it shows a woman with a small child walking towards a park where, according to the scenario, a man has been sighted near a play area carrying a gun. The woman receives the push notification, and turns around to head for safety.

Employees at Citizen headquarters scan the police radio, all the time listening out for details of crimes, and other occurrences, to be passed on to emergency response teams.

They record the nature of the incident and mark it on the app's electronic map. It appears on users' phones immediately, meaning that users have the information almost as quickly as the police.

Citizen.com assert that their intention is merely to warn about potential dangers at an early stage, and possibly encourage people to help where possible - for example, as first responders in the event of a medical emergency.