Facebook developed a system capable of recording ambient sound from mobile phones without the user noticing, Xataka announced.
The patent has been named “Broadcast content view analysis based on ambient audio recording” (Analysis of transmission content view based on ambient audio recording).
According to the explanation contained in the document, the software would start recording when different contents, such as TV commercials, emit certain sounds inaudible to the human being, but that the mobiles would detect.
As explained in Engadget, the user could be quietly watching TV when suddenly and without noticing his phone would turn on the microphone and start recording. It is assumed that, through detectable sounds only by mobile devices emitted during a commercial, they would turn on the cell phone recorder.