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About this Article
Written by: Tim Furnish
Written on: September 3rd, 2007
Tags: electrical engineering, energy & sustainability
Thumbnail by: Charles Beichman/CalTech
About the Author
In the fall of 2007, Timothy Allen Furnish was a mechanical engineering student at the University of Southern California Viterbi School of Engineering. His interests in engineering include learning new ways to solve mechanical problems and learning about new technology.
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Volume IX Issue IV > Motion Sensors

Motion Sensors in Everyday Life

Both radar and infrared sensors are used all around us in places we might not realize: public restrooms, shopping centers, and building alarm systems are among these.
Charles Beichman/CalTech
Figu​re 3: This is an infrared image of a Jet Propulsion Lab engineer holding a burning match. The image is color-coded to show differences in temperature: note the white and deep red in the flame and the engineers palm (where his warm blood vessels are close to the surface of the skin) and the blue of his cool glasses. This picture demonstrates that infrared images predominantly show heat energy and its distribution.

Public Restrooms

You may have noticed many new public bathrooms are switching to touch-free or automatic flushers, faucets, and hand-dryers. This is only possible with the use of motion sensors. Most of the motion sensors used in public restrooms today are infrared [9]. The faucets and hand dryers are activated once a change in infrared radiation is detected [10]. The flushers work by sensing a person approaching and departing, and then producing signals that correspond to both. These signals can be used to determine the correct time to flush [11]. Touch-free systems in public restrooms are growing in popularity because, after all, restrooms are not a place most people would want to be in contact with. How many times have you seen someone open the door with their elbows after washing their hands?

Shopping Centers

As mentioned in the introduction, motion sensors are also common in places such as the entrance and exit doors of grocery stores. Most of these sensors use radar and send out a high frequency sound wave and "listen" for bounce-back. If the sound wave returns at a different frequency, the sensor knows there is a moving object within the detection zone and sends a signal to open the door (Bircher Reglomat). Automatic doors are not only convenient because they provide easy access into a building, but they are also safer: the handicapped, elderly, or anyone carrying packages or heavy items can enter and exit much more safely using automatic doors [12].

Building and Home Alarm Systems

Another application of motion sensors that one might experience every day is the alarm systems in most buildings and in some homes. Both types of sensors, radar and passive infrared, have been commonly and effectively used for motion detection in alarms [2];[13] However, passive infrared systems have been used more recently in alarms, since the sensitivity of the sensor can be set to the temperature of the human body [6]. With this sensitivity, the number of false alarms is reduced since the sensor does not simply detect motion like radar sensors [2]. Both radar and infrared sensors can be connected to a sound alarm and cameras that will only turn on when the sensor has detected a change in the room [14]. Motion sensors in security alarms are very effective and are essential for most businesses. With motion sensors, a whole building can be monitored simultaneously.