Surveillance technology might be even more invasive than we think. According to new research published by a Norwegian student, some models of Bluetooth headphones can be used to track and identify their owners without their knowledge.

Bjorn Martin Hegnes, 35, who studies networks and IT systems at Norof University in Oslo, undertook a 300km cycle ride around the Norwegian capital over 12 days as part of his first year project. His kit included an omni-directional Wi-Fi antenna that could pick up Bluetooth signals from a distance of 100 yards away and a GPS device that could pinpoint locations.

Hegnes was able to collect around 1.7 million Bluetooth messages, over 9,000 Bluetooth transmitters and 129 headsets. 

He discovered that none of the headphones he analyzed during his cycles were implementing a security measure known as media access control (MAC) address randomization, which made it easy for him to pinpoint the exact locations of wearers.