Member Discussion

Glass Doors And Good Intrusion Detection

Hi all,

Looking for experience and strong opinions on detecting intrusion through glass doors.

We are looking to add access control to a large number of aluminum-framed glass doors. These are in large spaces and will be monitored after hours only. Motion sensors are not an option. We will be putting positions sensors on the doors one way or another.

Right now I am tending towards acoustic glass break sensors like the Interlogix ShatterPro. I am a bit concerned that these are inadequate though, as I have heard that even modern glass break sensors can be circumvented by cutting the glass or muffling the sound of striking glass. There will also be cleaning staff working with loud equipment every night.

I am looking at vibration sensors (like the Seco-Larm Enforcer) and glass shock sensors but these add a lot of complexity and install work. We can handle the occasional false alarm, but I don't want to double our work load by adding extra sensors to every door unless necessary; most of these doors are in pairs or in groups of four to eight, and ideally we would like to cover at least that many with each sensor.

Does anyone have dos and don'ts, or alternatives?


I suggest that you look at a 'curtain' type of motion detector, like the Honeywell IS216T. This category of PIR throws a largely-vertical, narrow pattern that is most sensitive to cross-traffic, and is made to work best in the situation you describe. I can see this installed so that the coverage is parallel to the door(s) you need to cover. It won't 'see' motion across the room. There are other models by other makers, of course, some made for very high ceiling mounting, such as inside the pull-down gate at a mall store.

Pattern illustration from DSC:


That's an interesting PIR, Michael. Thanks for mentioning it.

Have you thought about using PE Beam sensors behind the glass/doors?

PE beams are pretty miserable outside (false alarms galore), but given a climate controlled interior application, they might be a good fit to monitor a line of doors.

I think you could find a set to cover the full distance you need to cover for less than $200 from distribution lines like Optex or Takex.

Michael, Brian,

Thanks for the suggestions. I will take a look at the equipment you both linked to. One of my concerns though is the work done by overnight cleaners, including cleaning floors and the glass doors themselves.

We use the acoustical glass breakage sensors like the Interlogix ShatterPro in these applications all the time. You will occassionally get some false alarms if the cleaning crew makes noise that falls into the frequency range of the sensors, but these should be relatively manageable.

I would have concerns about using PE beams or curtain PIRs unless you could train the cleaning crew to stay away from the windows and/or turn off the detectors when cleaning the glass or the areas nearby. I would also expect that you may have other employees coming or going when the detectors are on and you would have to figure out some way to manage this.

In the old days we would simply use window foil....... :)

If people are working inside with the system on, you need glass break sensor—not curtain PIRs or photo beams. Also, know what type of glass you have and the size of the lite. Some detectors will not work on laminated glass in particular or below a certain size of window. Sound is also attenuated by curtains or shades. No problems, you just have to know what you are dealing with.

You may want to check out the Honeywell Felxguard line. They are a dual signal detector and known to be pretty well tested. GBS’s are a bit unique in their set up and testing method, so for your first install read the installation manual. You also need to buy one of their acoustic simulators for the testing. Not really costly, you just don’t want to do without it.

Now if you are really concerned about false alarms, stick a presence detector or motion detector in the space to shunt the zone when people are moving about on the inside. I think this would be pretty easy to do, given how sophisticated panels are getting these days (If not, a timer is only a couple of bucks). I actually did this in a very high end mountain retreat home and they have never had a nuisance alarm. The GBS are everywhere, along with alarm screens for windows they want to open.

Thanks all for the advice. Most likely we will be testing out acoustic sensors for this.

Hey Ryan:

Followup on this thread afterwards if you can. It would be interesting to get your feedback on what you choose to go with!

Thank you sir.