How To Detect People Coming In From The Drop Ceiling?

I have a customer that is nervous about someone coming in from the drop ceiling. The space above it is about 6 feet high, but there are air conditioning duct work going throughout it. He wants me to put a motion sensor there, but I am worried that the duct work will block it and make it that it wont cover everything properly. Is there a better way?


Where is this intruder going to stand and walk? There probably isn't anything up there that will support their weight.

I guess crawl on the ductwork. Supposedly someone tried it recently

There probably isn't anything up there that will support their weight...

That may not stop them...

Your average meth head is 80 lbs soaking wet....

I have wondered about this, I have several customers like this, several locations have steel beams that run across that someone could easily walk across. Getting to that location is not the easiest thought, it would likely involve busting through the fire wall of a neighboring unit

What is currently protecting the space below the ceiling tile now? Is it just a perimeter system, are there any internal cameras covering the inside?

High security locations require this and traditional motion detectors are installed. (SCIF/Tempest)

In the old days a $200.00+ device was needed, now they are so cheap.

Above ceiling was to detect intrusion during normal working hours while the regular system is disarmed.

Motion detectors are my recommendation. If, as UM3 above notes, the application is for use during business hours, the organization will need to be sure to modify their operational procedures/processes to account for the motion detectors. In other words, the HVAC worker (or the camera installer) should not penetrate the ceiling without getting clearance from the security group . . . in advance . . . in writing . . . with confirmation.

We're dealing with this right now. We install SRN200 PIR Detectors. They have been the most reliable for us in these situations. We have three above the ceiling. One is above a vault that is armed 24/7, the other two are programmed as supervisory zones, they will only display at the keypad. The security officer can at that time make the determination as to what they want to do if the sensor goes into alarm.

May consider something like the Honeywell IS216T-CUR, mounted on walls interior to the space just under the ceiling line. You can also mount them on the side of boxes if the size of the room is greater than what can be covered from the wall installation. Creates a narrow curtain, used for skylights, etc. Design must take into account the typical challenges of a motion sensor. Quite frankly if they have gotten that far undetected you have larger holes in your security design / processes than this addresses.

I would use PIR sensors inside the ceiling and magnetic sensors and even cameras aiming to possible entries to the ceiling

I had a customer install a Videofied system in the drop tile area and on roof of pharmacy. The first (and only) time they were robbed, the crooks entered through a hole in roof then hit the compounding room through the droptile. Existing analog cctv system gave no usable evidence...but proved to end user that one needs multiple layers of security.

I worked on a site once that had such a setup. After a thief had entered the washroom, then accessed the adjacent office by going through the drop tile and over the wall, they added a PIR on a 24-hour zone into the ceiling space over the washroom.

Unfortunately nobody working there at the time was aware of this and I got an earful of siren when I went into the washroom ceiling to pull an access control wire...

But in answer to "how would this work"... I'd say if someone is going to crawl ON the ductwork, you'd want to put the PIR above said ductwork. Realistically, there's usually going to be fairly limited areas with enough room for one to move about in a ceiling, whether it's above or below tin, between tin, between pipes.

There will probably be only one or two choke points between areas where they could enter (outside-accessible washroom, roof hatch, etc.), and areas of the store they'd want to access (storage room, office, etc.). Identify those choke points, and cover them.

Alternately, you could possibly add a couple cheap cameras up there, and set them to trigger either an internal I/O, or an I/O channel on the DVR, with just basic motion detection set to low sensitivity. You'll normally see little to no significant motion in the ceiling space, and any major change of lighting, whether from someone with a flashlight or someone opening a tile, will register as "motion" to the camera. Unlike a PIR, that needs an unobstructed "view" to work, a camera will register the change in scene anywhere within its FOV.

I'd say if someone is going to crawl ON the ductwork...

IN the ductwork as well ;)

You want cheap and easy? :)

get Optex 2000 with 6 wireless PIR

and put them above ceiling

output from receiver can be connected to alarm system

I see quite a bit of talk about using "Motion detectors". I have installed many systems mainly back in the day at Pawn Shops and Museums especially and found out that in the summer when the temp above the ceiling normally gets "HOT" they do not work as intended or at all. If you can alarm bar the vents, ducts and any other spot from a survey of the roof that may make it accessible to crooks. I have inverted "curtain" PIR's with some success in winter months, but dont kid yourself in the summer it ain't happening. Hell, put a stress sensor on the grid in the spots you assume may be a clever spot crooks could enter but mainly I would suggest "work out of the box" and create a solution for your circumstances.

"Hell, put a stress sensor on the grid in"

Nice to see old school knowledge :)

lots of ppl do not know about

If I remember correct it was using Wheatstone bridge to detect current variation?

+1 for idea

Lord Kelvin's bridge as well

#1, what is the shape of the area? How big is it?

Have you considered shooting photo beams around the perimeter? It may be tricky to get them mounted so they avoid all obstructions, but with some luck and careful aiming it seems like you could surround the area with beams that would break no matter where someone tried to enter from.

If you have a high value target, plywood and sheetrock the walls and ceiling in that particular room. At least you will slow them down somewhat and avoid someone slipping over an adjacent wall to get into the "office".