Abstract: A portable security alarm system includes a rechargeable battery and an infrared sensor to detect the presence of an intruder in a protected area. Three time delays are provided to allow the user to exit without setting off the alarm; to allow a legitimate user to disarm the system upon entry; and to limit the time that the alarm will sound. The system can only be disarmed by the entry of a multi-digit code that is kept secret whereas the device can be armed by anyone. The system is specifically designed to be resistant to spurious signals associated with electrical storms and is also designed to minimize power consumption. The system further includes circuitry to shutdown the alarm system when the voltage is low enough to risk damage to the battery. There are indicators associated with system operation including low voltage warning.