Putting name to stranger’s face: Tech Facebook, Google didn’t dare release

One afternoon in early 2017, at Facebook’s headquarters in Menlo Park, California, an engineer named Tommer Leyvand sat in a conference room with a smartphone standing on the brim of his baseball cap. Rubber bands helped anchor it in place with the camera facing out. The absurd hat-phone, a particularly uncool version of the future, contained a secret tool known only to a small group of employees. What it could do was remarkable.

The handful of men in the room were laughing and speaking over one another in excitement, as captured in a video taken that day, until one of them asked for quiet. The room went silent; the demo was underway.