Motion Sensor Alarm

Good examples of wireless motion sensors are automated doors at hotels or stores. They are a form of radar detection where the box above the door sends out a burst of microwave energy. When you move into that energy field, the energy bounces back and the door opens. Since these doors use radar they are a type of radar detector.

That's why a motion sensor alarm is perfect for your home security system. A small motion sensor mounted in strategic places inside and/or outside your home will set off an alarm if an intruder breaks into your house. Motion sensors are a key component of your home's security system.

There are several types of motion sensors:

Microwave Motion Detector

This detector type puts forth high-frequency radio waves that are then reflected by an object in their range. The motion sensor senses any pattern changes in the waves. That means the movement of an intruder in a monitored room will interrupt the pattern and an alarm will sound. (Note: Because these are highly sensitive motion sensor circuits, they can tend to create false alarms. When used in home security, they are often combined with another motion sensor type.)

The Ultrasonic Motion Detector

An ultrasonic detector has two components: one is a transmitter that emits very high frequency sound waves. In fact, they are so high that they cannot be heard by the human ear. The second component is a receiver that picks up the waves when they get reflected from the protected area. The intruder's motion in the space between the transmitter and the receiver changes the sound frequency which subsequently triggers the motion alarm.

The Passive Infrared (PIR) Motion Sensor

This is the type of sensor (also called pyroelectric sensors) used on motion sensor lights and home security wireless alarm systems. This is what is used on the automated doors described earlier.

To detect a human being the sensor has to be sensitive to a body temperature of human skin (about 93° F). Skin at this temperature emits energy within a wavelength of about 9 and 10 micrometers. So, the sensors are set to detect in the range of 8 to 12 micrometers.

The infrared light disturbs the electrons of a substrate which are detected and turned into a signal. Another thing to remember is that these motion sensors pick up rapid change in the amount of infrared energy, hence, motion. If you stand still, they will usually not be activated.

The lens used on a PIR motion detector is usually a Fresnel lens. The design of these specialized lenses has grooves which face the sensing element while the smooth surface is what you see. It retains its optical characteristics but is less thick than other lenses resulting in less absorption losses.

These lenses also allow for a wide field of view because the light emitted from infrared energy can be easily focused and manipulated.

So, when you are seeking to purchase a burglar alarm or home security system, ask the sales representative what type of motion detectors come with the system and how they work.

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