Where is that phone?

Tracking by cell site

As mobile phones move around, the network keeps a track of roughly where they are, so that any incoming calls can be routed to them. (see the How It Works section for details). This information can also be used to monitor the position of the phone. This location information is passed to the emergency services when a mobile phone used makes an emergency call, but it can be passed to other people.

This information can be used to provide local information to users. For example, to let you know where your nearest cash dispenser or pizza takeaway is, the network needs to have a good idea of where you are.

Some companies offer location tracking services for a fee. Normally this costs something like 25p or so per location update, but a few charge a monthly fee, possibly with some location checks included in the fee. Verilocation charge £5 per month including 10 location requests, with extra ones at 50p each. Fleetonline charges £2 setup, plus 30p per location update, but no monthly fee. It seems to be mostly geared towards company use, though.

Keeping track of location may be useful to a business with staff "on the road" or for parents concerned about the whereabouts of their children.

There are drawbacks, though.

Some would consider tracking an infringement of personal liberties. The companies offering the service avoid such criticism by requiring any tracked person to opt in by returning a text message giving permission to be tracked.

Normally, however, this permission is open-ended, and does not have to be renewed. A manager may give this permission before issuing a phone, so the employee using it has no idea that his or her location is being monitored.

These services track the location of the sim card in the phone, not the person. This means that it does not necessarily tell you where the person is, and it also means that the person being tracked may not be the person who had the phone when permission to track it was granted.

Of course, it may be that what is being tracked is the equipment, not the user. For example, it make a lot of sense to register your own handset with such a service so that if it is stolen or mislaid, you can find roughly where it is. Alternatively, you may want to track the location of something like a vehicle, so tracking the position of a phone in it tells you where the vehicle is.

Accuracy of location

Particularly in rural areas, the size of cells can be quite large, and so the location of the handset may only be accurate to about one kilometer. This may not be accurate enough for some uses, so there are other methods that can be employed.

In theory, it would be possible to be more accurate by using timing advance measurements to determine the distance of the handset from three known cell site positions, and give fairly accurate positioning, but this does not seem to be used at present.

To get accurate positions, the best way is to use GPS, which uses a system of measuring how long signals take to reach the GPS unit from several satellites in low earth orbit. There are a few hand-held mobile phones with GPS units built in, but not many.

There are devices available that combine a GPS and a mobile phone, specially designed to be concealed in a vehicle to be able to track its location. This system is used by some car rental firms, and is sold to people anxious to be able to recover their vehicle if it is stolen. For example, the £300 VTU007 Vehicle Location System from InfoMap uses GPS to work out where it is, and uses its built-in mobile phone to transmit this information back to the user. Verilocation offer a similar (but rather more sophisticated) equivalent on a three year lease at £45.83 per month.

Other solutions

Tracking the location of something like a vehicle does not have to use mobile phones. There are companies that use independent radio data systems to track the position of vehicles, mostly to recover stolen vehicles. An example of this is Tracker.

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