Best bet is to choose a system, and then get them to design the installation for you, with a quote for the materials. Then if your capable of following their drawing(s) install the system yourself, and get them or another registered company to do the testing & commissioning. Fire alarms are not rocket science, but they do carry statutory regulations....
It's the stat regs that carry the sting these days.
2012 saw nearly thirty "alarm" engineers prosecuted for a variety of things, not least incompetent maintenance, incorrect design, and so on.
I would also add that one firm, from memory, hung a guy out to dry who was supposed to be designing for them too.
We did a lot of work for a refurb contractor - who used an "all in one" design service - for the entire refit, including power, alarms, colour of the carpet etc. Initially, we threw back incorrect designs, having corrected them ourselves - until we discovered the design company was then simply re-marking up the drawings and charging over £500 for an amendment.... we very quickly moved to simply sending them back "does not meet requirements of an Lx system" - want to bet how quickly that design firm was on the phone to us?
You're dead right, though that pretty well anyone can install a fire alarm system..... to a degree, and you're dead right too that they're not rocket science - but the combination of ability, knowledge, and risk all have to be weighed.
Bottom line - even if a fire alarm system is NOT required - e.g. not mandatory in a building - if it's wrong, and an incident occurs where liability can be placed on the system, they WILL come after you. That's fact now.
Most fire alarm systems should be based on risk assessed - which is why Fire Risk Assessment should be carried out by a qualified Risk Assessor (and not the five question wonder you'll find on the HSE website)....taking into account other forms of fire protection, design of building, risk from ignition sources, and more. That bit is more scientific now, if not on the level of rocket science...usually. A competent FRA should be able to determine the need for, and category of, fire system required. From there, design is a matter of ability, knowledge, and competence.
Most manufacturers will be less inclined to design a system these days, unless you agree to indemnify them totally from any errors and omissions...and will not, in any case certify the design.
By far the safest option these days is to pass design to a (specialist) company prepared to certify the design, and underwrite the risk in that - and even then, such as ourselves, unless we can work from plans and/or a site visit, we'd only certify design if we were also commissioning. In this way we can be sure that what we're certifying is compliant and has been properly installed (justifies our risk, and saves potential heartache down the line) - we also do this to ensure installers have someone to turn to.
I turned up to a system we designed in 2009, to do the commissioning and found, despite our best endeavours, that the whole system had been run in with twin and earth....because the guy, by all accounts a decent sparks, had "always done it that way".... yep....not since 1998 though.
Potentially, these days, the hidden pitfalls are severe enough that it's fast becoming a case of you either do fire, or you don't....and if you do, cover for liability, specialist risks, wrongful advice, failure to perform, and professional indemnity are among the minimums you'll want.
The above are all key reasons that we're going for SP203 this year, and intend to keep it.
I'm not intent on scare-mongering by any means, quite the opposite - as you'll all see I'm happy to give all the advice I can too - but as I'm sure a few of the other "fire" guys here will testify, it's not the job it once was, and well, the heat isn't only coming from the fire, pardon the pun.
