This specification describes a method comprising detecting presence of a portable device in a vicinity of a first vehicle based on an identifier of the portable device which is detected at first user equipment, UE, located at the first vehicle, and further comprising causing transmission, from the first UE to a second UE located at a second vehicle in the vicinity of the first vehicle, of the identifier of the portable device and measurement data relating to the portable device and collected at the first vehicle, the measurement data being for use at the second vehicle to determine the location of the portable device relative to the second vehicle.