A switch having good maneuverability includes a switch case, a rocker-button unit having a hole therein and a rotating shaft located at a side of the rocker button unit and held at the switch case, and a push-button unit movably disposed in the hole. When the alcohol concentration is high and the operation state temperature is low, the generation of intermediate products, which are alcohol oxides contained in unburned alcohol mixed fuel, is promoted, and the intermediate products generated are trapped in an intake passage by opening an intake valve in the expansion stroke of the internal combustion engine. The system then generates a target EMI fingerprint for the target computer system from the target EMI signals.