The Gamma-Scout® is a Geiger counter. The principle is that high-energy radiation penetrates a “counter tube” containing a gas of a specific composition held in a vacuum. The radiation “ionizes” molecules, causing a small current flow which is counted at the cathode. Despite all the protective capacitors on the circuit board, strong high-frequency fields can cause ionization that does not originate from a,b,c radiation. The two most common causes known to us are a cell phone within a few centimeters of the Gamma-Scout®, which develops a relatively strong field when transmitting, or certain fluorescent lamps, which develop such a field on lighting up. Removing the cell phone from the direct vicinity of the Gamma-Scout® removes the interference.