An alarm system for an automatic transmission includes an alarm device and two or three control switches in a serial connection. One switch closes when the transmission selector lever is not in park position; the second switch closes when a condition preparatory to leaving the vehicle, such as door opening, is detected. The third, optional switch closes when an emergency brake is not securely engaged. Thus, an alarm is generated when the driver prepares to leave the vehicle with the transmission selector lever not in the park position. Redundant switches are disclosed for the first and second switches. Also, a holding relay is disclosed which maintains the alarm until the automatic transmission selector lever is shifted into the park position, by closing a shunt across the second switch whenever the alarm is produced.