The invention further advantageously provides a laser speed detector that includes circuitry to detect when attempts are made to evade speed detection by a laser speed detector.
By indicating to the police that a vehicle is transmitting high-intensity light energy, the officers can deduce that the operator of the vehicle is likely attempting to evade speed detection. Such an indication would also provide the officer with an identifiable error message if the light energy generated at the vehicle is of great enough amplitude to prevent accurate speed determination. Such an indication would also allow the sensitivity of the laser speed detector to be altered to ignore the high-intensity light energy.
According to the invention, therefore, a countermeasure detecting circuit and an associated method detect countermeasures taken at a target to impede speed measurements taken with a laser speed detector. The laser speed detector is operative to transmit light energy to the target and to receive light energy reflected from the target. Light signal detecting circuitry detects light energy of wave lengths corresponding to wave lengths of the light energy transmitted by the laser speed detector. Received-light signals of values representative of the levels of light energy of the selected wave lengths are further generated. A comparator circuit is coupled to receive the received light signals generated by the light signal detecting circuitry. The comparator circuit compares the values of the received light signals with a threshold signal. The threshold signal is of values representative of levels of background noise of light energy typically received by the light signal detecting circuitry. Comparison signals are generated responsive to such comparisons. The comparison signals are of values representative of times in which the light energy detected by the light signal detecting circuitry exceeds levels of background noise by at least a selected amount. Control circuitry is coupled to receive the comparison signals generated by the comparator circuit. The control circuitry detects when the comparison signals are of values indicative of countermeasures taken at the target.