A German website has been set up to allow people to check whether mobile phones are switched on and within reception range without informing the phone subscribers who are being checked on.

Called SMS Gateway Ping, the service is offered as a web demonstration by the Berlin startup company gate5, which specialises in location-based wireless and web applications. At the moment it's only a test, which the general public cannot use.

The service is named for the ping (packet internet groper) network utility, which determines whether a particular IP (internet protocol) address is online by sending out a packet of information and waiting for a reply.

In gate5's version, the user enters a mobile phone number in a field and clicks a button marked 'Ping', upon which the system responds, after a brief delay, with the message 'The telephone is switched on', or 'The telephone is switched off or has no reception'. The window promises an automatic update every 10 seconds and, indeed, a test showed that it quickly registered when a mobile phone which had been previously off was switched on.

There is the possibility that this type of service could soon be used to locate mobile users without their knowledge. Staff at gate5 were, however, not immediately available for comment.

The system works via the SMS (short message service) protocol supported by GSM (global system for mobiles) networks widely in use in Europe. A test showed the system works, at least, for numbers in Germany, the UK, France, and the Netherlands.

Users are not informed that their phone is being pinged, though a signal that can be picked up as a disturbance by nearby radio receivers indicates network activity on the part of the handset.