You can save energy with motion sensors by rigging them to your lights in low-trafficked areas of your home. They won't save as much money or energy as replacing standard light bulbs with energy-efficient ones will. Most people who give a hoot have already made the switch or are making the switch to CFLs anyway.  Motion sensors can be a way to add a bit of energy-savings frosting on the top of the CFL cake. 

Where Motion Sensors Will Help The Most

Motion sensors are best used in areas of the house that get little foot traffic: The garage,  the bathroom, the stairwell, the porch, the front door, basement, the attic, the laundry room. When a person enters one of these rooms, the motion sensor will catch their movement and switch on the light. When the person leaves, the light will go out after a set period of time. This ensures that lights, like the basement light, do not get left on needlessly for hours or even days. They are also a great benefit for the front door. No longer do you have to keep the light burning when expecting company. If you go grocery shopping at night, you may opt to leave the light on in order to carry the unwieldy bags without incident. 

Motion sensors can eliminate the need for those types of situations as well. 

The Downside of Motion Sensors:

Motion Sensors do use a bit of electricity and some may require batteries. If you are a super contentious person, someone who always remembers to turn off the light when leaving a room, motion sensors may not save that much energy. They may actually use a bit more.. A flaky absent-minded person like myself would probably benefit from motion sensors, but a methodical, circumspect character like Batman, for example, could probably get by without them. 

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