Why go GSM? If the garage isn't too far from the house you can go wireless detectors & have your house alarmed too (assuming you have phone line / naked dsl). Stay away from the cheap stuff, if it false alarms all the time it's just going to annoy you & your neighbours then you stop using.
As a market GSM/GPRS is the next step up from standard monitoring / line protection so it carries the price tag, aus is also a very small market for alarms so we pay should anything need to be changed in design/manufacture.
Almost all locally sold stuff has 2 year warranty, Bosch has 3 year. For some reason the warranty rates seem relatively high with alarm systems so there is a good reason to go local.
There is a cheap GSM/GPRS capable system that we are starting to trial which comes as a kit with detectors, can't say anymore at this stage. I personally was interested in this for my place but now going for more of a "feature" alarm (touchpad with lcd display for photos etc).
