I'm not sure what time of system your looking at, but mine was just 4 motion sensors in the main access points of the house, but the system doesn't get installed until after handover these days. It's still paid for by the builder etc, but you have to setup a time and date with the installer to get it done. All because of safety concerns etc (same with safes etc - builders, apparently, only do the housing or fitting for one now - not that actual safe too).