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Anyone who has ever watched a crime thriller has probably picked up on a key trick to avoiding having your mobile phone conversations overheard: Simply switch out your phone’s SIM card to an anonymous account and then freely plot without a care in the world. If law enforcement doesn’t know the phone number you’re using, they can’t eavesdrop.
But according to a team or researchers at the Technical University of Dresden, that technique may not be so foolproof. The team led by Jakob Hasse has discovered that every phone has a unique radio frequency (RF) fingerprint that law enforcement officials could identify by passively scanning the airwaves, according to a New Scientist report. Just as each human fingertip has a unique set of friction ridges, every phone’s set of RF components — amplifiers, oscillators and signal mixtures — all have minute variations that introduce unique error patterns into their signals, Hasse told the New Scientist.
It’s not the combination of components that produce the variations, but the components themselves. No two amplifiers or oscillators are exactly alike. Each contains a different set of minute inaccuracies introduced by the manufacturing process, according to Hasse. Two iPhone 5s could have the exact same hardware and could have been built side by side in the same factory, but because of the differences in their signal patterns, a properly configured scanner could distinguish one from another.
That means law enforcement — or anyone else with the proper gear — may someday be able to pick your phone’s unique signature out of the airwaves if they’re within in range, no matter what SIM or carrier you happen to be using. Hasse’s team conducted tests on 13 handsets in its labs and was able to identify the correct phone 97.6 percent of the time.
As for how useful such technology would be in surveillance is debatable. Unlike a regular mobile phone “tap,” it can’t be used to track a phone across the entire network. Once the analog signal hits the tower’s base station, it’s converted into a digital signal, presumably destroying its unique RF fingerprints. But if a surveillance team knows where its target is is likely to be, it could use a scanner to isolate his phone’s airborne signal, discovering in the process what new SIM card he may be using to evade detection.
Feature photo courtesy of Shutterstock user fredredhat