The security system provides an aircraft security system capable of protecting both single and multiple engine aircraft. Variations of the present system prevent unauthorized starting of protected aircraft and activate an alarm when engine starting it is attempted. Embodiments of the system draw no power from the aircraft when the security system is armed and in no way interferes with the normal starting or operation of the aircraft when the system is disarmed. Embodiments of the present system can activate an alarm when an aircraft's doors or panels are opened. Embodiments of the present invention can activate an alarm when installed equipment or other devices are tampered with or removed from their housings.