A detecting magnetic coil is mounted adjacent the authenticity-determining magnetic coil of an electronic slug rejector to distinguish between authentic coins and any copper slugs which might cause the authenticity-determining coil to produce an output which closely simulates the output which that authenticity-determining coil produces in response to authentic coins. The signal from that detecting coil is used to control the accept/reject gate of that electronic slug rejector; and it will effect movement of that gate to "accept" position in the event it detects a non-cupreous object but it will not effect such movement of that gate in the event it detects a copper slug.