Security sensors for the detection of intrusion are generally known. On a basic level, intrusion detection may be accomplished through the use of window or door switches. On another level, intrusion may be detected in open areas through the use of one or more motion sensors.
The detection of motion may be accomplished via many different types of devices. One type of motion sensor is referred to as a PIR (Passive InfraRed) sensor. PIR sensors operate on the principle that the body temperature of an intruder allows the intruder to stand out from a different temperature background. In this case, the infrared signature of a human intruder may be used to activate an alarm.
Other types may rely upon ultrasound or microwaves. In some cases, the different types of motion detection sensors may be used together (e.g., PIR and microwave).
It is desired in the security field to more reliably detect entry of an intruder into a protected space. A common method of accomplishing this is to use dual technology motion detectors consisting of a Doppler microwave frequency motion detector and a passive infrared (PIR) detector. The PIR detector senses infrared radiation (IR) from the intruder while the Doppler microwave frequency motion detector transmits a microwave frequency signal and detects a change in the return signal due to the presence of an intruder.
The use of PIR and microwave sensors in combination offers a number of advantages over the use of the individual devices by themselves. For example, PIR sensors may not operate very well where an ambient temperature is close to the body temperature of an intruder. On the other hand, microwave sensors have the disadvantage of being able to detect motion outside the protected area.
The combination of the detectors may be used to eliminate false alarms by using the inputs from both types of sensors. In this case the combination may eliminate false alarms due to the microwave motion detector detecting motion outside the protected space or from the microwave detector detecting vibration of an object within the protected space. The combination also eliminates false alarms from a PIR detector due to non-human heat sources such as a heater. Also, the detected Doppler signal from microwave sensor can be used to detect intruders when the ambient temperature is close to the body temperature of intruders.
Microwave sensors require the use of a directional antenna that transmits microwaves across a secured area and receives reflected signals. However, the detected area of a microwave detector is typically larger than the protected area of PIR detector. In order to get best performance, it is necessary to match both microwave and PIR protected areas. In order to do this, it is required to adjust the sensitivity of the microwave sensor. This is a time consuming process. Accordingly, a need exists for better methods of setting up microwave intrusion detectors.