glassbreaks vs. motion detectors

[kaohao]

Is there a certain protocol for positioning and distribution of these devices? For example, it seems redundant to have window sensors, a motion detector, and a glassbreak detector all in one room or in close proximity to each other. Any thoughts?

 

[SterlingDonnelly]

Glass break detectors activate when they "hear" the actual frequency of broken glass. Door/window contracts activate when a door or window is opened and the contact separates from the magnet. A motion activates when it "sees" a change in passive infrared energy in the room.
 
All three devices have pros and cons and are suitable for different types of applications/intrusions.

If you have a sliding glass door with just a contact on the door, you would be unprotected if someone threw your patio furniture through the glass opening and just walked in without opening the door, the door contact would offer no protection. If you used a glass break and no contact, then you'd be vulnerable to break-ins where they open the door and don't smash the glass.
 
Motions are more of a catch all but because they are usually off in "Stay" arming mode, you aren't protected for perimeter intrusions as you are with glass breaks and contacts. Also motions can be prone to false alarms from pets.
 
I hope this helps you decide which sensors to use in each area of your home so that you get the type of protection you and your family needs.

 

[Del91574]

The summary is reasonably close, however GBD's need 2 criteria to generate an alarm, not just "hearing" the sound of breaking glass. They would need to hear the flex (think initial thud, which also contains the event of the glass bending prior to shattering) and the sound of the glass itself breaking. Better detectors have better signature analysis which equates to better false alarm rejection. Even better units self-adjust their sensitivity and continue to do such on routine basis vs. down and dirty trimpot or dipswitch settings.
 
You need to equate perimeter vs. interior protection and how the system is intended on being used. If you're intending on a well designed system, you would have contacts which detect forced opening (or you leaving points open, resulting in an open invitation) and backups to those devices.

PIR's are only going to detect when someone is already within the protected space. A properly designed system detects them before they get to the inside. Motion only based systems, or those with minimal contacts installed on a couple doors (mass market install) offer a false sense of protection and detection as the intent and goal of a security system is to detect intrusion prior to the intruder being within the protected space, with PIR's being a backup/redundancy to offer further protection.