A group of researchers from the National University of Singapore and the University of Yonse (Korea) developed the method to identify the hidden inclusion of a microphone on a laptop. To demonstrate the work based on the Raspberry Pi 4 board, an amplifier and a programmable receiver (SDR), a prototype is assembled, called TickTock, which allows you to identify a microphone with malicious or spy software for listening to the user. The technique of passive determination of the inclusion of the microphone is relevant since if, in the case of a Web-camera, the user can block the recording simply by sealing the camera, then it is problematic to turn off the built-in microphone and it is not clear when it is active and when not.
The method is based on the fact that when the microphone is operating, the circuits transmitting clock signals to the analog-digital converter begin to radiate a specific background signal that can be caught and separated from the noise caused by the operation of other systems. According to the presence of electromagnetic radiation specific for the microphone, we can conclude about the record.
The device requires adaptation for different models of notucks, since the nature of the emitted signal is highly dependent on the used sound chip. To correctly determine the activity of the microphone, it was also necessary to solve the problem of filtering noise from other electric circuits and take into account the change in the signal depending on the connection of the laptop (autonomous work or work from the network).
As a result, researchers managed to adapt their device to a reliable determination of the inclusion of a microphone on 27 out of 30 laptop models, production Lenovo, Fujitsu, Toshiba, Samsung, HP, ASUS and Dell. Three devices that the method did not work with were the Apple MacBook 2014, 2017 and 2019 models. Researchers also tried to adapt the method for other classes of devices, such as smartphones, tablets, smart speakers and USB cameras, but the efficiency turned out to be noticeably lower – out of 40 The tested devices tested were established only by 21, which is explained by the use of analog microphones instead of digital, other connection schemes and shorter conductors emitting an electromagnetic signal.