Motion Detector Placement - Forced Warm Air Heat - Open Window


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Old 11-03-13, 08:33 AM
R
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Motion Detector Placement - Forced Warm Air Heat - Open Window

I'm considering installing a SimpliSafe (brand probably doesn't matter) wireless burglar alarm system which relies heavily on passive infrared motion detectors. Since my house is heated with a forced-warm-air system, I'm concerned about the placement of these sensors. Will a heat register (which changes temperature but which doesn't move) trigger a motion detector? Manuals I've reviewed on the Internet warn not to place motion sensors over baseboard heat radiators but make no mention of forced warm air registers which behave quite differently.

Motion sensors would also be placed in the cellar (the point of entry for previous burglaries). Unfortunately, the warm air supply duct runs down the center of the cellar ceiling for the entire length of the house. Will a motion detector be affected by this duct's heating/cooling cycle? I should be able to place the sensors so that the furnace is not in their sensory path but it will be difficult to avoid this main duct unless a seperate motion detector is used to monitor each of 4 windows, door and a staircase.

Lastly, I was considering placing a sensor in the living room and directing it at the windows and front door. If one of these windows were left open at night and a car (with a hot engine) drove down the street (about 40 feet away) would that be enough to trigger the sensor through the window and screen? I note that my outside security lights are finicky about this. Unless they are finely adjusted I could do jumping-jacks within 10 feet without result ... but just let a car drive down the street and they turn on.

Thanks for any real-world help you can provide. I've gotten conflicting guidance from the well-meaning folk who have not actually performed an installation themselves. Any real-world alarm installers out there?
 
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Old 11-03-13, 08:43 AM
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The actual ductwork will not trigger the motion sensor.
We usually try to install motion detectors to see across windows... not directed at them.
Try to avoid curtains which can be blown by a forced air system.

Actually the brand has a lot to do with performance. A more expensive unit uses multiple methods of detection..... not just infra red. They also use microwave/ultrasonic technologies.
 
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Old 11-03-13, 11:55 AM
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Hello: Robert

IMO, a motion sensor should be the second line of defense. Not the primary...:NO NO NO: Especially the battery motion detector types. A motion sensor should be a backup to the door/window sensors.

The brand you mentioned is excellent. Why? Because each door/window sensor has a blue LED light that flashes each time the door/window is opened or closed. That feature lets you know it's working and the battery isn't DEAD! Seeing is believing. Without monthly testing...

That brand also has a chime feature. Base chimes each time a door/window is opened/closed. Lets you know an entry point allowed access even though system is turned off. Some systems do not have this feature.... Some systems do not have a HOME setting either...

That brand does not rely heavily on the motion sensors.... Nor should you in my opinion. Comes with one motion sensor only. It has no means of testing it unless you carry with you the portable keypad, activate the system and cross the sensor. If system activated sensor working. But don't count on any of them working unless hard wired with a RED blinking light indicating operation.

IMO, based upon you explained and desired needs, buy plenty of door/window sensors. Install them on each door/window. Use motion detectors only as a backup to them. Each component can be individually controlled in the base station.

Read that products web site fully. Motion sensor operation and distances explained. Any door/window sensor not in contact, even when system is off, is noted on the keypad. Display will advise. Example: One sensor opened.......Exception is motion sensors....

 
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Old 11-09-13, 11:05 AM
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Thanks for your input.

Just to clarify, I'm not skimping on the door/window contactors in the portion of the house where the windows open. The windows at the back of the house - the point of entry for the past two burglaries - are fixed in place. Each time the burglars broke out the 3 panes of glass as well as the woodwork between them and entered through the resulting opening.

But you did give me an idea. It's possible that I could string a weighted wire across these windows and attach the magnetic part of an entry sensor to the wire. With some careful placement of the wire and the rest of the sensor, it could be arranged so that pushing the wire away from the window would pull the magnetic contact away from a sensor. Alternatively if the wire was cut, the weight could pull the 2 halves of the sensor apart. Similar to Ademco's old #176 Two Way Trap.

Thanks again.
 
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Old 11-10-13, 07:08 AM
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Hello: Robert

Trip wire. EXCELLENT IDEA... Brilliant improvised method too. Something one would not get from an alarm company installation. Only one that is intended to be (DIY) self installed.

Done correctly there should be no way to defeat the system for the magnetic sensor(s). Then the motion sensor can be located in an area where motion can be sensed if entry was made. Any unobstructed area that must be used to gain house upstairs from basement/cellar to upper level access.

Each sensor, motion or magnet can be set separately and independently of each other in the alarm brand system mentioned. Magnet piece works even if it had to be scotch taped onto wire(s).

Motion sensors sense heat differentials and some also motion. Motion sensors should not face any register or area where the heat difference would change between ambient room temp to warmer. Nor face a fan which is on producing motion.

Nor should they be more then 5 feet above floor level even though installers place them higher to be out of the way or unobstructed, etc. The distances vary only slightly between battery operated units installed by major nationwide companies. Most sense 30 feet forward and 180 degrees wide. An open window with autos passing by not likely to set if off.

Choose a system, install and advise. We all learn from each other here on the site.

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