text: The first large scale British civil defence issue was the Geiger–Müller counter Meter, Contamination, No. 1 set — stock number "5CG0012", of 1953. It had 0–10 mR/hour range with external probe and headphones. This was designed to use two 150 volt batteries, although later they were fitted with a vibrator power pack which used four 1.35 volt mercury cells or, alternatively, a mains electricity power pack. Many of these units remained in service until the 1980s.  There was also a Mk. 2 model which used rubber connectors and cable for the probe unit, compared to the Plessey connectors of the Mk.1.
  This used cold-cathode valves and very high impedance circuitry throughout to extend useful battery life as long as possible with the existing technology.