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Home Made Alarm Systems?
screwBrinks! asks: "I would like to begin a new project to do during those long and boring weekends. I thought about creating an alarm system in my apartment which would be connected to my computer. Then, if there is any intrusion, it would page me or phone me. I also want to be able to see a live report from the web and some other goodies. I have no problem doing the software part, but I don't have much experience with building hardware. Have any of you ever built such a system? If so, what would be your recommendation? I know much of this may already exist prebuilt, but I really would like to make as much of it as I can, for fun. I have no problem against using prebuilt infrared detectors, prebuilt door contacts, and the like as long as they aren't X-10 products."
I know somebody who did this recently. The results are very impressive, and he managed to do it all very cheaply.
First step was picking up a mini-security camera from the local electronics store. Cost $150AUD and is the size of a bottle cap. It's a CCD based camera with 12V input and standard TV composite output. It uses a pinhole instead of a lens to get the size so small. It's only black/white but it also picks up infrared! Auto-adjusting brightness. The picture quality is quite amazing.
Run a coaxial cable + 12V power cable (low amp wire) to the camera. The cable can be really long - this guy is running it over 20 metres. Plug the other end of the coaxial cable into a BT878 TV card on the PC. The TV card was $100AUD. The PC was $300AUD. You need at least a Celeron-2 processor. The 12V power supply is $20AUD pre-built from the electronics store.
Next, install Linux! You need the "motion" software package. It records MJPEG (?) but only records changing frames. It also puts a useful highlighted rectangle around the section of the frame that moved.
Finally (and I don't think he's done this step) you write a simple script to rsync the motion/MJPEG output directory to a remote server. You can use "stat" on the directory to determine if there are new frames: record the "modified" line, compare it on subsequent stat commands, any difference means there are new frames so call rsync! You could easily stick an email in there as well to alert somebody.
The setup is very impressive. The picture quality is simply incredible. Because the CCD camera detects IR you could even use it in the dark with some IR leds to illuminate the room with "invisible light". A number of people have shown interest in building their own after hearing/seeing about the original setup.
I found this on Google using the search term "computer serial port remote data plans"
So you have to add glass breakage detectors - which is already four times the effort of a single infrared motion detector. One of the best looking - best performing passive infrared detector is the sharpshooter from Sentrol It is built on an asic and incorporates years of professional experience.
The beauty of the PIR is that it is highly effective with minimal false alarms. The sun moving across the sky, casting a hot spot on an interior wall for example may trigger a camera system, as may the a/c system moving a curtain. A good pir - properly placed in an outside corner looking in is very trustworthy.
If you want easy - ITI makes the best wireless system - now in their third design iteration of asic based transmitters - they have far surpassed the garage door opener days of wireless. Professional over the counter system
ITI Home
One problem with PC based security is battery life. Many burglars either shut off the power or take advantage of power outages to improve vulnerability. Professional systems can run several days without power.
The weakest link in most security systems though isn't the detectors or the batteries - it's the phone line. The salesmen learns quickly to ignore this point because the solutions are expensive, and once raised - their isn't much point to paying 30 buck a month for monitoring when a simple screwdriver can unhook the telephone. In most places the phone company insists on placing the connection outside, where they and anyone else can easily get to it when you're not at home.
The Siren is completely useless - worn thin by the mass production of car alarms with their characteristic sequence of pseudo police siren sounds. You can forget anyone caring about your house until about two hours later when it finally makes them angry enough to want your head shrunk and placed on a pole.
Cellphone connections are expensive - as are radio systems in most places. People have tried direct connections, but if the wire gets broken - too aften they just send the repairmen out to fix it - so what's the gain? Constant IP monitoring would generate the same kind of false positives everytime At&t cable internet goes down - every police car in town would be dispatched to check on "suspicious loss of service".
Thus you need a staged warning system with an off-site mayday server. Put infrared detectors outside especially on the side of the house with the service connections - connect them to lights and enjoy the benefit of a house that welcomes you. In Addition, have the system send a mayday signal to the server whenever activity is detected around the house. Maintain this connection until either the house is entered and the system turned off - or the connection is cut - thus triggering a genuinly suspicious disconnection. In this case - the mayday server calls you - then the cops - your mother-in-law etc . . .
Bottom line - and the reason i left the business - the most effective part of the system is the stickers on the window. The technology is mostly smoke and mirrors.
AIK