Motion Sensors?

Motion sensors use infrared beams that are transmitted out, bounce off walls and furniture and the sensor picks up what is bounced into it.  You DO NOT have "heat sensors" as well.  The infrared (IR) IS the same spectrum as heat.  So it's the same thing.  When the sensor detects a change in the signal strength for the IR spectrum coming into it (by something breaking a beam), it sends the signal to trigger the alarm.  Weight and size has nothing to do with it.  Anything that blocks light and moves in the room and changes the beam pattern will set off the alarm.

What needs to happen is the motion detection system needs to be recalibrated so that the IR transmission and reception is all above a certain height.  You have to allow for the dog to say, jump onto the couch.  So basically, you only have motion detection from four feet and higher.  The beams are invisible to all forms of visible light so no burglar would no about it and thereby crawl underneath them like in 'Entrapment' (although if you're going to be robbed, you could do worse than having THIS crawling along your floor in the middle of the night!) 

I went with glass break detectors and door and window sensors rather than motion sensors in areas where my two cats live and motion sensors elsewhere. The sales guy said the cats won't set them off, the installer said they would.

I think the sales guy is like mine was: ignorant of the technical reality. Get it right fast, because if your police are like ours, the first false alarm is a freebie, but after that, they start charging.

second that - the salesman was feeding you BS!

motion sensor senses motion - unless your dog is stuffed and next to the  fireplace, he'll set it off.

the only other option is to set the sensors at a much higher level, e.g. 5 feet, assuming your dog is under 5 feet and/or doesn't walk around on 2 legs.

in our place in Chicago, we had the same thing and never we able to use the motion detector because even though we were told our two 25 lbs dogs wouldn't set it off - movement is still movement.  Plus, we had stairs coming into the living room, which also set it off.

we were fine with window and door sensors and sadly enough - came into great use as on 3 different occasions, people tried to break in.

I'd clarify the motion sensor issue with ADT before your stuck paying for a service you can't use.  (speaking from experience)

The one article I read said they will basically go to the front door and knock.  If noone answers go to another entrance break in go to the master bedroom and living room, avoid the kids rooms since there is nothing valuable anyways.  If someone answers the door they ask if "Bob (or some other random person) is there" and then just leave.

The article also gave suggestions to leave valuable in Kids room or some other room the crooks won't go.

I no longer have my alarm because I just don't feel it will really do any good unless they break in at night and I can do something myself.

What are your thoughts?

No.  The motion sensor can measure weight approximately.  The sensor is an infrared sensor that detects the heat given off by a body.  The size of the signal is a rough measure of weight.  Contrary to what another poster said, the sensors do not send out a beam and look for a reflection.  They sense the heat from the object itself.  To detect motion, the sensitive region of the cell is divided into cells  (think of a digital camera with the image frame divided into small regions).  The "motion" detection is really two adjacent cells being activated in sequence.

TW