DIY burglar alarm using cheap PIRs, soldering iron and PC ?

[Simon]

Hello -

I'm currently adding a bit of security to my house by buying some cheap wireless PIR sensors and receivers from

, interfacing a PC to them, and switching on lights, sending email alerts, posting webcam pictures to a website, etc. when activated. It's going well so far.

I'd be interested to know if anyone can see pitfalls in this approach, eg.

- PIR manufacturer going out of business and not being able to get compatible receivers/transmitters

- burglars who carry radio jammers (does this happen outside of crime novels?)

- What am I losing by not using sensors intended for alarm systems

- Are inconspicuous PIR sensors less of a deterent than a big bell-box?

- I'm thinking of installing one of these at a property that already has an "Anglian" branded wireless alarm system - are they likely to clash?

Thanks

[VisionSet]

What are you doing for the data logger?

[Owain]

Microsoft or Linux based OS? ;-)

Quite possibly

Unlikely. More likely to hack your kernel these days.

Internal PIR sensors are no deterrent. By the time Mr Scrote The Thieving Scumbag is close enough to see your PIRs he's in your property.

Gawd knows, but why not rip the whole lot out and install a proper wired alarm system for a fraction of the price.

Owain

[VisionSet]

So you have your PC on all the time. I'd definitely want to avoid that if possible.

[Simon]

I use the PC's serial port to monitor the state of the wireless receivers, Java to poll the port, send the alerts and control the webcams, and a database to log the data. It's very DIY.

[VisionSet]

If you are doing it in Java then why not buy a board with JVM on it. about

50 quid, (prob less now). It comes with a one wire port for your interfacing.

[Andy Hall]

Microsoft doesn't make any OSes.....

[Simon]

The standalone mains-powered PIR sensor has a row of Knight-rider style red LEDS, which should attract the attention of anyone peering in through a window. OTOH, they'd look silly and possibly reduce security if the PIR was installed outside.

[meow2222]

An old P1 laptop sounds like a good candidate, pref with a backup spare.

NT

[Harry Bloomfield]

Simon explained :

Buy enough plus spares.

Extremely unlikely, even if they already knew about the special system.

I would suggest the biggest pitfall is likely to be the reliability of the PC itself - the likelyhood of it crashing. For really critical stuff which needs to be able to restart the system should it crash, consider a 'watch dog' system. PC sends a regular pulse signal out to a discrete 'watch dog' circuit, if the circuit fails to see a regular pulse from the PC, it reboots the PC. The pulse is generated by the PC from running software, sent out via a bit on one of the ports.

Nothing to stop you adding a big bell box and flashing lights.

Clash, unlikely if the PIR uses the PC wireless network frequencies

2.4Ghz and the Anglian 432Mhz licence free - no.

[Harry Bloomfield]

It happens that Simon formulated :

What about mains failure? No mains, no working alarm system.

[Owain]

By the time Mr Bawbag The Burgling Bastard is close enough to peer into your windows he's also close enough to steal your carkeys or pour petrol through your letterbox.

You'd probably be better off with gravel and pyracanthus in the front garden.

You could put the Knight-rider style LEDs into a dummy bell box though.

Owain

[Owain]

Sorry, once more with a comma.

Microsoft, or Linux based OS?

Owain

[woodglass]

What's your address (for when you are finished) ?

[badger.badger]

70 cms, nice and jammable!