1. A vehicle including an arrangement for monitoring objects in or about a vehicle, comprising: an infrared source from which modulated infrared illumination is emitted into an area in or about the vehicle; a receiver arranged to receive infrared illumination reflected from an object in a path of the modulated illumination; and circuitry coupled to said receiver and said source and arranged to compare a phase of the emitted modulated illumination with a phase of the received illumination at a common frequency to determine a phase difference between the modulated illumination and the reflected illumination, said circuitry being arranged to obtain three-dimensional information about the object from the determined phase difference and monitor movement of the object based on data obtained from the three-dimensional information.