Abstract: Embodiments of the invention provide apparatus (100) for detecting an erroneous measurement of a range of a target object 20 from a subject object (5) comprising: wireless transmission means (111) for transmitting a signal (111S) having a first frequency from the subject object (5) to the target object (20); detector means (113) for detecting a portion of the signal (113S) reflected from the target object (20) back to the subject object (5); range determination means (131) for determining the range (202) of the target object (20) from the subject object (5) by reference to a time of flight of said portion of the signal (111S), (113S) from the transmission means (111) to the detector means (113); and rate determination means (131) for determining the rate of change of the range (203) by reference to a difference between the first frequency and an apparent frequency of the reflected portion of the signal (113S) detected by the detector means (113), the apparatus (100) being arranged to provide an indication (20

Abstract: An apparatus for monitoring one or more target objects in an environment external to a host vehicle by means of at least one sensor, the apparatus being arranged to trigger at least one action responsive to the detection of prescribed relative movement between the host vehicle and the one or more target objects. The apparatus is arranged to determine whether the at least one sensor is correctly aligned with respect to the host vehicle whereby, when the apparatus commences monitoring of the environment, the apparatus is arranged not to trigger the at least one action until the apparatus has determined that the at least one sensor is correctly aligned.