Abstract: Methods and apparatus for optimizing the response of a radiation detecting device such as a cold cathode discharge tube are disclosed. The tube is energized at each instant of repeated sequences of successive time instants which are fixed in time relative to a time datum, and held energized for not more than a respective activation period following each said instant, consecutive activation periods being mutually separated by recuperation time periods. Response of the device during each of the activation periods is sensed for, and a warning output is produced only when the device responds during each of the activation periods of at least one sequence. The lengths and number of activation periods during each sequence are selected to increase the probability of a warning output being produced in response to radiation of a predetermined wavelength relative to the probability of a warning output being produced in response to background radiation.