There's pros & cons.
I have installed a "Securistyle" wireless system, as I used to act as a minor local agent through my company, so got a big box full of freebies. Oh most of it seems to be fitted at home now, but it would not have been too pricy anyway, compared to some.,
Dead easy to install DIY if you have a screwdriver, no chasing of wall & drilling of holes.
It works a treat.
Installation is minimal when it comes to PIR detectors dotted around, magnetic door switches, fire alarm things, etc, all sending a signal to the box in the hallway if there is a problem.
No mucking about with bloomin' bell wire running everywhere. 128 frquency settings to pick from, 10,000 codes to dis-arm the box on authourised entry, 15 secs if someone gets it wrong, immune to power failure etc.
Bad bits : you still need to run a power supply to the controller, and from there with cable to your outide alarm boxes.
(it sets it off in any cable is removed or cut.)
Biggest thing is that each unit needs a little battery.
As per a standard ceiling fire alarm, though, should be ok for a year or two. The thing therefore needs to be checked, say once a month.
I would recommend a good wireless system, Rab, the initial cost for the bits & peices may be a bit higher, but overall a cheaper, better looking installation job.
Best of security with it !