Blu Eye monitors frequencies used by the encrypted TETRA encrypted communications networks used by government agencies in Europe. It doesn’t allow the user to listen in to transmissions, but can detect a radio in operation up to one kilometer away.
Even if a message isn’t being sent, these radios send pulses out to the network every four seconds and Blu Eye can also pick these up, according to The Sunday Times. A dashboard-mounted monitor uses lights and sounds to alert the driver to the proximity of the source, similar to a radar detector interface."
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