In movies, there are often scenes where the protagonist swaps out the SIM card of their phone to avoid having their calls intercepted, allowing them to speak freely. However, researchers from Dresden University of Technology have recently discovered that this method may not be entirely reliable. Jakob Hasse, the team leader, stated that they found every phone has its own unique radio frequency (RF) signature. Law enforcement can potentially identify a specific phone by monitoring these RF signals in the airwaves.
Similar to how each person's fingerprint has distinct ridges, the RF components in each phone (such as amplifiers, oscillators, and signal mixers) create very small but unique deviations in the signal. This concept might exceed the general understanding of mobile phone signals for most people, but Hasse explained that these deviations originate from the components themselves. Just like there are no two identical amplifiers or oscillators in the world, slight differences occur during the manufacturing process. Even two iPhone 5s produced on the same production line can be distinguished by specific monitors due to their slightly different RF signals. Hasse’s lab has already tested 13 handheld devices with an astonishing accuracy rate of 97.6%.
Nevertheless, this new identification technology cannot exert its power across the entire network like conventional call-tapping techniques. At this stage, if such analog signals are converted into digital signals through transmission towers, the RF fingerprint will be erased.