Exposure indicator with continuous alarm signal indicating multiple conditions

An exposure indicating apparatus comprising:

• at least one sensor having at least one property responsive to a concentration of a target species;
• and
• a processing device generating a concentration signal as a function of the at least one property, the processing device including a single signal indicator activated as a function of the concentration signal, the processing device further including driving means for continuously driving the indicator at one of a first signaling rate indicative of a readiness state of an exposure indicating apparatus operating within predefined design parameters, a second signaling rate discernible from the first signaling rate indicative of an exposure indicating apparatus operating outside of the predefined design parameters, a threshold exposure signaling rate indicative of the concentration attaining a predetermined threshold concentration, and a varying exposure signaling rate that varies as a function of the concentration signal after the predetermined threshold concentration is attained.