Abstract: Apparatus to detect tampering with a totalizing device on a fuel dispenser with a totalizing device acting to keep a running total of fuel dispensed from the fuel dispenser and including an electric circuit containing at least one coil that will emit a magnetic pulse responsive to a condition consistent with proper totalizer operation, the apparatus including an arrangement for sensing the presence of the magnetic pulse and generating a signal responsive thereto and an arrangement for causing an alarm responsive to absence of the magnetic pulse.