If you intend to get an intruder alarm installed I would go the professional route and not the DIY route; equipment intended for DIY installations is poor at best and I personally wouldn’t recommend any.
You’re best off for looking for an installer in the Yellow Pages who is NSI/NACOSS or SSAIB approved as they have to undergo regular inspections to maintain their memberships. They can design a system tailored to your needs and not what is available from a limited selection from the DIY market; the added benefit would be that your insurance company would recognise the alarm and set your premiums accordingly.
No doubt somebody will recommend a wireless/X10 type system, but I would steer clear as the equipment reliability is variable at best.
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