Abstract: A voltage level detector circuit comprises an amplifier for amplifying the electrical output signal from a detection device, a pair of comparators for comparing the amplified electrical output signal with a respective threshold signal, wherein each comparator is adapted to change its output state when the amplified electrical output signal exceeds the respective threshold signal, and a pair of threshold processors responsive to a superimposed noise or interference component of the electrical output signal from the detection device, or of an amplified version thereof, and adapted to provide the comparators with respective threshold signals which vary with the superimposed noise or interference component, so as to maintain a relationship between the amplified electrical output signal and the threshold signal which is substantially independent of the superimposed noise or interference component.