To answer your questions alarms protect an Area or area's,these can each
consist of a number of zones.
A zone is a specific sensor under SSAIB & NACOS rules and may perform any of
a number of different tasks.
( entry/exit ,panic,smoke ,fire,alarm etc.)
An area is a group of zones linked together under a specific setting code.
In practice take 3 flats in the same unit each flat is an area with its own
access code to the alarm in the entrance hall.
Inside each flat are 3 zones ; the door ,living room ,bedroom.
In domestic cases area;s are not used (often) and the control panel
determines the number of zones that can be added and how they are
As for your alarm I have never fitted one but have seen them in operation
.For a budget system they are ok but as a DIY system have their limitations.
As posted Risco Group supply the trade with alarms and their systems are
excellent with lithium batteries giving up to 3yrs life and panels all
containing autodiallers (just plug into a bt line).
To be fair ADE,Scantronics,Bosch and others also supply excellent radio
Your choice is cost ,installation,& reliability.
All modern alarms these days have very few false activations (most are
customer error or installation faults)
And whilst no alarm in the world will prevent you from being robbed a
reliable one will deter some thieves,alert good neighbours ,give piece of
mind and even call you to tell you it's been activated.