Hello Lisa
Firstly, Welcome to the forum!
There are numerous house alarms available thesedays and mainly 2 types of house alarms for DIY installation. A hard wired system and a RF system.
The hard wired Alarm normally consists of a mains powered control unit with a bell/siren unit, complete with rechargable back-up batteries in the control unit and siren. The door and window contacts and the Passive infrared detectors (PIR's) are wired in and therefore apart from replacing the rechargable back-up batteries every couple of years, the system is virtually maintenance free.
The drawback with the hard wired system is the amount of wires which need to be run, which can often be untidy and I've known people's cables to get chopped by carpet fitters, etc. Also because numerous wires need to be run, the installation can take much longer
Personally I prefer the Wireless-Radio frequency (RF) type. The Control unit and each door contact, PIR, Panic push, siren box and other accessories have their own batteries. There are few wires to run and the installation can easily be completed in a day.
The drawback with a RF alarm system is the fact that the batteries will require replacing ever 2 years or so.
My personal choice is the Yale HSA 3500 system.
The Yale is very reliable. I have one myself. The control unit alerts you when each accessories battery requires replacing. The HSA 3500 also connects to the telephone. You can program the unit to dial your mobile phone in the event of an alarm activation. You can dial your alarm when you're out and check the status for added peace of mind. There's even a "Listen in" facility where you can hear anyone in your house. In fact it is packed with features, I could spend all day telling you about.
Most of all as I said though, it is RELIABLE. Your neighbours will be pleased too.
Yale also offer a telephone helpline which I have used and I can say are very good.
The accessories for the Yale can work out expensive, but you can add them as time goes by. Yale offer Door contacts + add-on magnetic contacts, (though if you have UPVC windows, I'd recommend you purchase additional stick-on magnetic contacts from Maplin Electronics Stores) PIR's, panic pushes, remote keypads, extra bell boxes/sirens and even Smoke detectors. Yes you can even use the Yale as a Fire Alarm.
Please feel free to ask me if there's anything else you'd like to know, either by PM or openly within the forum.
All the best
Lemonade