Mobile phones are believed to have played a crucial role in tracking down those arrested for alleged involvement in the wave of attempted terror attacks.
Police recovered phones from the two Mercedes cars which had been left in the centre of London. They are thought to have been left in the vehicles as detonators for the bombs.
This could have been done by setting the phone’s alarm or by ringing the handset from some distance away.
But for the phone to work it had to have a Sim card – the small chip provided by the phone company to the subscriber. It carries a wealth of information, such as whether it is on a pay-as-you-go contract or monthly subscription.
It also carries the phone number, enabling police to get details of calls made from the carrier.
The phone itself will store recently dialed calls, unless the history has been wiped. A call to a landline would give a name and address.
The same information would probably be available if the owner had contacted a mobile subscriber as well.
It is believed that this could have helped police identify the address in Glasgow, which was raided just ahead of the attack on the city’s airport.
Similarly it is possible that phone records helped identify Mohammed Asha, the neurosurgeon who was arrested on the M6.
But the role of the mobile phone does not stop at identifying suspects, the signals they send also enabled police to track their movements as they passed the nationwide network of masts.
This network is so extensive that it is being considered as a potential option for a national road pricing scheme, because it makes it possible to track the movements of a car remarkably precisely.
The role of mobiles in tracking the movement of suspects has been laid bare in a number of high profile cases.
At Soham, the silent signals being transmitted from a phone belonging to one of the murdered girls enabled police to place them at the house of Ian Huntley, who was subsequently convicted of the killings.
In another murder trial, police were able to trace the movements of the killers of an Asian businessman from the crime scene at Sutton in south west London, around the M25, to one of their homes.
Even without making any calls a suspect would have been easy to follow – provided he did not switch his phone off.
But having been identified, it would also have been possible for police to supplement this with details of his car, with its number plate details being fed into another database, which in turn could have been tracked by roadside cameras.