Imagine sleeping soundly and suddenly awakening to a piercing sound. More than likely your motion detector alarm has performed its job well of alerting you to danger and causing the intruder to make an about face. Such an occasion justifies a motion detector alarm as an ideal part of security systems. It is not uncommon for today's homes to have alarms systems to detect movement outside and or inside the house. The motion detector uses high frequency radio waves and when they are unstable the alarm is activated. The alarm's purposes are to alert occupants of an intruder, warns the intruder to leave immediately and to alert the authorities. Alarms systems that employ motion detectors are everywhere and may be as basic as someone coming through a door and triggering chime sounds, the automatic opening of a door, or signals sent when light beams are interrupted or energy level changes.

The motion detector works by using infrared sensors, photoelectric (light) and ultrasound or microwave sensors within a specific area. It can even detect differences in sound energy. Each type will trigger an alarm that lets others know that someone has entered the monitored area. The average home interior motion detection uses a beam and light sensor. If someone passing through it interrupts the beam, the control box is alerted and the alarm is sounded. Many modern motion detector alarms are located inside of a control box that is a part of the alarm circuit. The control box is responsible for monitoring the system and sounding the alarm when prompted. Once the alarm is activated it can only be turned off after entering a code on the keypad. Whenever the code is entered improperly or not within a certain amount of time, another alarm is sent out using the telephone circuit to call for the security service or police.

Motion detectors are a standard feature of industrial security systems that require a more sophisticated system than those for the home. On the advanced security systems that are used in commercial or high-end homes, the detectors work by sensing energy changes within its field. An alarm is activated when the passive infrared (PIR) detects human movement that emits heat or energy. PIR senses energy or heat from humans. (Animals also produce heat). The heat is called infrared and the system itself is passive because it does not activate unless there is a change in its field. The PIR works by measuring the heat change against standard energy levels. This measure is in place to avoid triggering false alarms. It is important to note that the microwave or ultrasound systems are the more expensive forms of motion detectors.

Security is very important, whether personal or industrial. Security systems with motion detectors and alarms are available in a wide price range. When choosing the best home alarm system, you should consider your security needs and budget. A simple system is easy to install yourself or a professional can install a more sophisticated system. The more advanced systems are usually available through monitoring companies that charge a monthly fee. Research and comparison-shopping are always best when looking for a security system.