Apparatus comprising: at least one processor; and at least one memory including computer program code which, when executed by the at least one processor, causes the apparatus: to detect (S3.1) presence of a portable device in a vicinity of a vehicle based on an identifier of the portable device which is detected at user equipment, UE, located at the vehicle; to cause (S3.3) transmission, from the UE to one or more other UEs each located at a different other vehicle in the vicinity of the vehicle, of the identifier of the portable device and measurement data relating to the portable device and collected at the vehicle, the measurement data enabling the location of the portable device relative to the one or more other vehicles to be determined at the one or more other vehicles; to enable (S3.4) receipt, at the UE located at the vehicle from the one or more other UEs, of the identifier of the portable device detected in a vicinity of each of the one or more other vehicles and measurement data relating to the portable device and collected at the one or more other vehicles; and to determine (S3.7), at the vehicle, the location of the portable device relative to the vehicle based on the measurement data collected at the vehicle and the measurement data collected at the one or more other vehicles; wherein at least one of transmitted measurement data collected at the vehicle or the measurement data collected at the one or more other vehicles is indicative of: a distance between the portable device and a vehicle at which a UE which collected either the transmitted or received measurement data is located; and a direction of the portable device relative to a vehicle at which a UE which collected either the transmitted or received measurement data is located. at least one processor; and at least one memory including computer program code which, when executed by the at least one processor, causes the apparatus: to detect (S3.1) presence of a portable device in a vicinity of a vehicle based on an identifier of the portable device which is detected at user equipment, UE, located at the vehicle; to cause (S3.3) transmission, from the UE to one or more other UEs each located at a different other vehicle in the vicinity of the vehicle, of the identifier of the portable device and measurement data relating to the portable device and collected at the vehicle, the measurement data enabling the location of the portable device relative to the one or more other vehicles to be determined at the one or more other vehicles; to enable (S3.4) receipt, at the UE located at the vehicle from the one or more other UEs, of the identifier of the portable device detected in a vicinity of each of the one or more other vehicles and measurement data relating to the portable device and collected at the one or more other vehicles; and to determine (S3.7), at the vehicle, the location of the portable device relative to the vehicle based on the measurement data collected at the vehicle and the measurement data collected at the one or more other vehicles; wherein at least one of transmitted measurement data collected at the vehicle or the measurement data collected at the one or more other vehicles is indicative of: a distance between the portable device and a vehicle at which a UE which collected either the transmitted or received measurement data is located; and a direction of the portable device relative to a vehicle at which a UE which collected either the transmitted or received measurement data is located. to detect (S3.1) presence of a portable device in a vicinity of a vehicle based on an identifier of the portable device which is detected at user equipment, UE, located at the vehicle; to cause (S3.3) transmission, from the UE to one or more other UEs each located at a different other vehicle in the vicinity of the vehicle, of the identifier of the portable device and measurement data relating to the portable device and collected at the vehicle, the measurement data enabling the location of the portable device relative to the one or more other vehicles to be determined at the one or more other vehicles; to enable (S3.4) receipt, at the UE located at the vehicle from the one or more other UEs, of the identifier of the portable device detected in a vicinity of each of the one or more other vehicles and measurement data relating to the portable device and collected at the one or more other vehicles; and to determine (S3.7), at the vehicle, the location of the portable device relative to the vehicle based on the measurement data collected at the vehicle and the measurement data collected at the one or more other vehicles; wherein at least one of transmitted measurement data collected at the vehicle or the measurement data collected at the one or more other vehicles is indicative of: a distance between the portable device and a vehicle at which a UE which collected either the transmitted or received measurement data is located; and a direction of the portable device relative to a vehicle at which a UE which collected either the transmitted or received measurement data is located. a distance between the portable device and a vehicle at which a UE which collected either the transmitted or received measurement data is located; and a direction of the portable device relative to a vehicle at which a UE which collected either the transmitted or received measurement data is located.