Abstract: The present invention is a wireless security system. Each alarm sensor contains three magnetoresistive sensors and that are capable of detecting the three-dimensional vector of a magnetic field. Preferably, the sensors detect the orientation of the door or window based upon the earth's magnetic pole. The three-dimensional vector output of the magnetoresistive sensors is received by a microprocessor on-board the alarm sensor. The microprocessor continuously compares the magnetoresistive sensors output with the maximum allowable position of the door or window. If the magnetoresistive sensors output exceeds the maximum allowable position, the microprocessor will signal an alarm, which is transmitted to the network controller via a transmitter on-board the alarm sensor. If an intruder attempts to disable or override a sensor, the alarm sensor will transmit a tamper signal to the network controller.