After the door and window alarms, indoor motion detectors are a primary feature of good, effective home security system. Unfortunately, many people are leery of motion detectors. They either think they are "too" hi-tech and therefore not affordable, or they've had negative experiences with too many "false alarms" by accidental triggering.

The truth is, motion detectors are available based on a variety of technologies and covering a wide range of prices. These devices have also become much more dependable and efficient as technologies have advanced.

Here are the various kinds of indoor motion detectors available..

Infrared -- Though magnetic sensors are the most common in home security systems (used for door and window alarms), infrared sensors are the most frequently used in motion detectors. These sensors are designed to detect radiated heat and are often referred to as PIR sensors, or passive infrared sensors. The fact that this particular technology is so cheap and reliable has made it standard choice among most security systems.

Microwave -- Microwave sensors are able to detect movement by emitting microwave energy. Microwave energy does have its shortcomings. For instance, it is able to penetrate walls which allows it to detect motion in other rooms. The most frequent application of this type of sensor is in automatic doors as seen in many retail businesses. But, combined with other technologies (see below) it is still quite useful in home applications as well.

Dual -- One of the frequent issues in indoor motion detectors is with the family pets. These sensors have to be able to distinguish between the movement of a family member and that of an animal in the house (say a cat or a dog). These dual sensors utilize microwave and infrared technologies and are able to ignore movements that should not trigger the alarm system.

Ultrasonic -- These sensors can be one of two types. They can either emit high frequency sound (called an active sensor) or they can detect sounds (called a passive sensor). Being among the most sensitive motion detectors available they are also among the most costly. For that reason alone, they are not typically not found in home applications.

Shock -- Typically these are not thought of as a motion detectors because they are not detecting the movement of people, but of air. More commonly known as glass break sensors, these actually detect the shock wave created when a window is broken and so they are often referred to as "glass break sensors". These devices are sometimes called "sound" or "acoustic" sensors. Many times they are used as a redundant monitor for the magnetic sensors typically used for windows.

Though the best case scenario is to keep the potential home intruder out of your home, sometimes they do gain entrance. When that happens, it is critical to be alerted to any "unauthorized" movement in your home. Indoor motion detectors play a vital role in home security.