A motion detector is an electronic device that can sense movement. It contains special sensors that are sensitive to changes in either light or sound, and transform these disturbances into an electric signal. They are usually connected to other devices that are designed to alert someone if they sense movement. Such motion detector alarms are important part of any security system, whether for home or business use. These sensors may be connected to a classic burglar alarm that creates a loud sound (80 decibels or more) meant to attract the attention of the homeowner or security personnel if it senses motion. Some alarms will dial one or more telephone numbers, such as the police or a security service. They may also turn on cameras to capture video of the moving object they detected.

Basically, there are three types of motion detectors. Passive infrared detectors sense body heat. The advantage of these detectors is that the sensors don't emit any energy, so they have low long-term costs. The sensors in ultrasonic motion detectors send out to high-frequency sound like the sonar of Navy ships. The ultrasonic signal bounces off everything in its field. A change in the echoes of this sound tells the detector that something is moving. Microwave motion detectors work much the same way as the ultrasonic ones, except that they use microwaves in place of ultrasonic signals. They work a lot like radar guns. While all of these devices have their own advantages, dual-technology motion detector alarms are the best bet. These dual-technology devices combine one or more different sorts of motion detector into one alarm. An alarm is only sounded if both the sensors detect motion. This greatly reduces the occurrence of false alarms. These alarms are usually very energy efficient as well, as the lower energy alarm is the only one running most of the time. If it detects motion, it wakes up the other alarm and asks it to confirm the motion. People with pets should not be worried about installing a motion detector system.

Many modern motion detectors have special functions that allow them to ignore moving pets as long as they weigh less than 80 pounds or so. Although these detectors are an effective way of making homes and businesses secure from crime, they have many other uses as well. Many businesses use them to save on energy costs. Using detectors that time how long motion has been stopped for in public toilets allows those businesses to turn off lights when there is no occupant. Offices and libraries often install such devices to make sure that unused portions of the building are not being wastefully powered. Parents of small children and people taking care of elderly parents or grandparents make use of motion detectors to prevent nighttime wandering. People who are traveling often take along wireless alarms for their motel rooms.

There are many different kinds of motion detector alarm equipment. Some sensors are wireless, and can be placed anywhere. Some are wired into the house. Some are for indoor use only. Some are built to stand conditions outside. A comprehensive security system needs both indoor and outdoor motion sensors. That is the best home alarm system to have. There are many different brands selling many different products, each meant to provide different coverage and options. A simple wireless sensor can cost as little as twenty or thirty dollars. Multiple sensor units meant to cover a wide area, or that are connected to a phone system, can cost around $100. Extensive hardwired security systems covering large areas both indoors and out can cost over $1,000. While these sorts of security systems are usually installed by professional security companies, cheaper units can be picked up at stores like RadioShack, or any big box store.