To professionally fit an alarm one has to be a member of schemes to monitor and there are strict rules about having two separate devices trigger before it auto calls the call centre. As a result those used in the trade are very different to those used for DIY fitting.
Also what do you want it to do. My sons alarm includes the door bell and also when set also puts central heating into lower heat so reducing heating bills when leaving the house. Some can ring ones mobile when some one rings door bell and alarm set.
Fire and intruder can be integrated there are some very complex systems. So you as the user have to decide what you want. The problem is unlike a car where some one rocking the car will set it off with most alarms some one has to get inside the house before it goes off by which time likely too late.
Bell boxes are cheap so just mount bell box on wall don't bother to wire it. It is a deterrent rather than alarm.
I've been looking at a number of diy alarms but having had a quote from a professional installer the difference in cost isn't that great and the company is SSAIB registered so the not very large additional cost is in this instance worthwhile I think.
Incidentally I already have a dummy box which didn't seem to deter them!
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