To provide a sound apparatus and an anti-theft method which can effectively prevent thefts such as thefts from vehicles.

An abnormality detection sensor 170 detects specific operation which may be related to a theft of apparatuses arranged in a vehicle and reports the detected result to a security control part 222. The security control part 222 receiving the report determines whether the specific operation is detected in a situation other than allowable situations or not. When the determined result is YES, the security control part 222 sends an alarm tone output command to a sound output control part 210. The sound output control part 210 receiving the alarm sound output command allows a sound output unit 130 to output a harsh sound giving an unpleasant feeling to persons and corresponding to measuring sound source data at the maximum volume.