Most PIR scensors manufactured now, especially devices that are used soley as alarms , are equipped with more than 1 type of sensor that it will use to determine whether or not to ALERT or not. And yes this is true for most every model ive seen in the last two years, including the "cheap ones". For instance I'm sure you have heard of the driveway alert system as seen on tv. Even this inexpensive device uses two methods of detection using its infrared capabilities...motion AND change in temperature. This is an excellent feature because the sensor must detect both simultaneously in order to alert you. This will cut the chances down considerably. Especially after you do a little homework, mixed with a little trial and error, and get it placed in the perfect spot. I have a very similar version of the driveway alert system. The ONLY difference is my receiver, or centralized part that IS the alarm can have an unlimited number of transmitters, which are the devices that actually senses motion and temp change. And yes these are cheap and EXTREMLY ACCURATE!! So accurate that a warm blooded animal has NEVER walked within range and it not alert me about it. And they detect through through tree lines, bushes, and other places wher someone would try and hide. The infrared sensors are $9.00 each and receivers are $15. Consider this, budget permitting, purchase 2 receivers, placing one to alert using the "ding dong" mode and use it to program sensors you will place outside. They are 100% waterproof. I have sensors that have never been protected from any of the weather Arkansas could throw at them for 2 yrs plus that work as well now as the day I bought them. The other receiver should be set to the MUCH MORE uninviting sound labeled "alarm". Use those sensors programmed to it inside your home. Remember this, a false alarm is usually a error in placement of the sensor. Read the instructions to find the max range of detection, and angle of detection. Then I suggest pulling up google earth. Go to view your property and use the ruler to determine the best placement. The ruler measures distance and angles. Its the best way ive found for camera placement as well. Works great especially when you want 360 degree home protection which is difficult enough to do depending on yard size, landscape, shape of home, ect...You certainly will want to maximize your equipment's abilities based on specs included in instructions. A birds eye view of your home and surroundings will take the guesswork out of determining effective placement. Simply use the ruler to draw the lines for your devices angle of field of view, drawing the line out to its max distance of detection. Everything within the lines will be the detection zone. Use a couple dif colors for the lines should you use multiple devises so not to get confused. Hope this helps those of you interested in home and personal protection. Feel free to ask if you have any other questions on this subject.