The company first previewed the feature in September. Until now, though, it was only available as part of a seven-city pilot that started in December.

While unstated, the feature is clearly a response to the murder of student Samantha Josephson, who entered the wrong car after hailing an Uber. Although Uber has long displayed the car model and license plate number of drivers after hailing them (it started sending push notifications to this effect in April), not everyone pays attention -- and those that do might still hop in the wrong car. PIN codes theoretically prevent similar tragedies, although the voluntary nature may limit use to people who are already cautious about the cars they enter.