Information about spy equipment sold by UK defence contractor Cobham to US police departments has been leaked.
The catalogue, labelled "proprietary and confidential", features a number of gadgets designed to track phone users and monitor and control communications by intercepting messages, jamming transmissions and pinpointing geographical location, according to The Intercept, which has obtained a copy of the 2014 document.
Among the devices on offer are International Mobile Subscriber Identity catchers, which allow eavesdropping on phone calls and messages and which Cobham claimed can pinpoint a users' location to within a metre.
They allow controllers to gather unique identifiers from a large number of phones in the vicinity. US police authorities routinely deny the use of such devices, which essentially create fake mobile networks to which phones automatically connect.
The document also lists a range of devices designed to cause cellular blackouts and to take control of mobile phones, some of which have a range of several miles.
Portable "direction finding units" may be hidden in a vehicle or in clothing and used to track the whereabouts of a phone user by officers on the move.
The use of bulk interception equipment by the police is a concern to civil liberties activists, who insist that they effectively treat everyone as a suspect.
"By design, these devices are indiscriminate and operate across a wide area where many people may be present. Such indiscriminate surveillance systems are not targeted in any way based on prior suspicion," Richard Tynan, a technologist at Privacy International, told The Intercept.
"As we move to a more connected world where cars, toys, fridges and even implantable devices contain miniature cellphone technology, the capability to cause harm using one of these devices becomes ever greater. It is unacceptable for our modern critical infrastructure to be so vulnerable to such interception."
Tynan also complained about the lack of standards governing the use of such technology and the secrecy surrounding its deployment.
"It is vital that the international standards that underpin our communications are built to the highest security standard possible," he said.
Many in the US are worried about the increased militarisation of the police, who are using equipment designed for the battlefield.
Activists and politicians have called for more control over the way that the $1bn annual police equipment budget is spent.
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