You probably are here because you are considering installing or upgrading a home security system / burglar alarm. Getting an idea of which product fits your basic requirements before you go shopping for prices should give you an understanding of what you get for your money & what each system key features are.
If you are renting, there is the problem that you may have to leave the alarms behind if & when you leave the property, unless you get a system that is capable of being easily moved.
If you are seriously considering moving home in the not too distant future, then consider how much value for money you are getting. Unless you are doing it just for the peace of mind alone, is the work worth the investment?
But on the plus side, the fact that your home already has a good security alarm fitted could make it more marketable & attractive to a potential buyer.
Doing it yourself is an option, especially in terms of initial cost savings. You can also buy a system yourself, then hire a contractor to fit it.
Buying the product from a home security company is probably the way to go if you want a system that meets any type of regulatory standards.
The work will also come with warranties & the hardware with product guarantees.
When getting quotations, get them in writing, get them from at least 3 independent companies and always look to use professional & trade accredited companies.