In 2014, Facebook filed a patent application for a technique that employs smartphone data to figure out if two people might know each other.
The author, an engineering manager at Facebook named Ben Chen, wrote that it was not merely possible to detect that two smartphones were in the same place at the same time, but that by comparing the accelerometer and gyroscope readings of each phone, the data could identify when people were facing each other or walking together.
That way, Facebook could suggest you friend the person you were talking to at a bar last night, and not all the other people there that you chose not to talk to.
However, Facebook says it hasn’t put this technique into practice.
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