PIC based Burglar Alarm controller
As with all things 'Security Industry', the average home alarm system costs an arm and a leg. The control unit usually supports a couple of wired 'zones' and maybe one or two 'PIR' sensors. 'Output' (in addition to the 'alarm' sounder) is typically a set of normally open relay contacts. One 'zone' will incorporate a 'entry delay' (which means the alarm waits for you to enter the disarm code) = allowing the 'snatch' thief to be in and out before the alarm sounds = whist on the other zones (and PIR's) the alarm triggers on the first 'glitch' (so no 'false alarm' prevention).
Some systems incorporate a battery back-up. Since the assumption is that loss of mains power = intruder with wire cutters, many alarms trigger on loss of mains, as you will have noticed when all the alarms in your street sound off on an actual mains power cut. Some even trigger on the first mains 'glitch'
Design your own PIC control unit and you can 'customise' it for whatever functions you require and build in suitable 'anti-false alarm' delays
Non-standard functions for the PIC
Whilst standard alarms come with PIR's etc. they typically have no 'pre-alarm' fucntionality. A PIC controller could be used to activate flood-lights etc. and power-up camera's etc. 'on first detect'.
The PIC can also be programmed to detect 'suspicious behaviour' = for example visitors who cross the boundary but don't approach your front door - or approach the door but don't use the door bell - or those who spend 'excessive' amounts of time on your property apparently 'doing nothing'.
The PIC can keep a count of the number of photo's taken and set a 'flag' to indicate that memory cards etc. need to be cleared
What's an alarm for ?
Deterrent - visible security components - alarm box, PIR sensors and CCTV camera's - are all intended to deter the would-be intruder.
Apprehension - a sounding alarm is designed to attract attention thus encouraging the intruder to leave quickly before they are discovered and apprehended
Identification - any decent system should gather evidence (usually in the form of images) that can be used to identify of the intruder (and maybe lead to the return of your property)
Many would-be intruders will 'case the joint', often in daylight, even approaching your front door to examine locks etc. before attempting to break-in, usually after dark. This means your system must be running during daylight hours and gathering CCTV footage of anyone crossing your property boundary. Fortunately few criminals leave more than a day or two between 'casing' and 'breaking = so the storage required for 'archival' footage is not excessive (although you do need to cover the longest holiday you are likely to take)
A better "CCTV" Camera
The quality of the average CCTV camera is appalling. The 'standard' was designed to allow 4 CCTV camera's to be recorded onto a simple (American TV) standard (480x720) Video Tape = in other words each camera had a resolution of 240x360 pixels. This was just enough to tell the difference between 'nothing happening' and 'some-one there' - but totally useless for identification purposes (unless the criminal could be convinced to position himself 'head and shoulders' in front of the camera - and then remain stationary for long enough !)
More 'modern' systems allow a single 480x720 camera to be used (instead of 4x 280x360), however even this is almost useless for ID purposes = at LESS THAN half a mega pixel it's 10x worse than the most ancient digital camera !
Today's CCTV camera's are capable of supporting full HD 1920x1080 = 2 mega pixels (at a mega price), however this is still 10x lower resolution that todays digital cameras
Rather than waste your money on useless low-resolution CCTV cameras, why not dig out your old digital camera and see if it can be 'pressed into service' ? Even a 10 year old camera will offer at least 4 mega pixels (i.e. twice the resolution of todays 'top end' = mega-wxpensive, full HD cameras)
If you don't have an old digital camera you are willing to 'sacrifice', visit your local Charity shop = ancient digital camera's at 4 Mpixels & above can often be found for less than £10. Even cheaper sources would be 'FreeCycle', your local Car Boot or Jumble Sale. Slightly more expensive (due to postage) would be eBay
Ideally you want one that accepts standard batteries - those with proprietary batteries often incorporate extra contacts (eg. for charging control or 'power low' detection), which may prevent you using a mains power block. You also need to remember that older camera's used older digital storage media = the older SD card standard was limited to 4GBytes (so any above 4Gb i.e. all modern SDHC cards, likely won't work at all).
You should avoid any Camera using 'Sony Memory Sticks' (or other obsolete media that can't be found today at any sensible price) unless you already have the media (or the camera has an 'AV output', of which more later)
Camera 'trigger'
You need a camera that's equipped with an 'external shutter control' socket (some allow continuous shooting when the external control button is 'held down', however a PIC controller can issue multiple 'single shot' signals to cameras without continuous shooting capability)
One drawback is that the typical digital camera is not designed to be 'powered up' for days on end (even if you feed it from a mains power supply), however since it's not going to be used for anything else, you can try replacing the manual 'power on' button with a pair of relay contacts driven from the PIC (so long as the camwera's power-on delay is not too long)
The ideal camera will have the ability to 'insert' the date (and, ideally, time) into the photo = this is vital if your photos are to be used in evidence
If the camera can't add date/time it may be possible to position a digital clock within the 'field of view' (eg on the 'dash panel' of your car)
Boundary 'detect'
One thing a PIC controller can do is and activate camera's etc. when someone crosses your property boundary - detected by a PIR, IR beam or some more mechanical means (such as a magnetic gate switch etc).
This allows you to monitor all visitors, irrespective of their intentions, and means your camera's etc. are all 'up and running' well before any intruder tries to gain entry. It also allows you to activate flood-lights etc. to 'welcome' the visitor (no decent camera works in the dark - those useless CCTV camera's with a well advertised 'IR mode' just generate poor quality B&W)
Door trigger
About the one place where a CCTV camera can deliver a decent photo is when the visitor is standing directly in front of a camera 'built into' the door.
The typical CCTV camera has such as tiny lens that building it into the door is no more intrusive than fitting a peephole 'spy eye'
Again, a PIC controller can 'monitor' the door bell and use that to control the camera (if a visitor leaves without ringing the door bell, the PIC controller can 'flag up' this suspicious behaviour)
Recording from a camera
Some digital camera's came with a 'TV output' (AV out) - which was intended to allow you to 'show off' your photo's on your TV. However some could be set to use the TV out as a 'live view', which would allow you to plug the digital camera into a CCTV recorder = or it would if you selected the appropriate menu option and left the camera powered-on continuously