Source: http://www.fastcodesign.com/3025361/coul...

Called the Ko-TAG system, the on-board positioning system placed in a car relays radio signals to a specific sensor carried by pedestrians. By bouncing signals back and forth between a transponder carried by a pedestrian and the sensor within the car, Ko-TAG can compute how far away the person is, and what direction she's moving in, allowing the unit within the car to predict whether a collision is likely. Using this information, a driver could be alerted to a person striding out into the street from behind a large truck, for example, hidden from view, and if a collision is imminent, it can trigger the car's emergency brake, stopping the vehicle before the driver even sees the pedestrian. Almost anything that can send or receive signals could be set up to be a transponder, even, cell phones, which pretty much every pedestrian is carrying around anyway. 

Obviously, no one wants a car to brake every time a pedestrian stands near the edge of the sidewalk, so the potential for false alarms is high. Ko-TAG’s creators aren’t entirely transparent about how they can prevent this, though the research lab’s website indicates the risk assessment algorithm would prevent false alarms: “With the data obtained from the tracking of detected objects, such as direction of movement, distance and speed, the situation can be evaluated comprehensively and—in combination with suitable movement profiles--the collision risk can be assessed precisely.