ADT u need to pay them annually or monthly, just for their calling service.
If u use other alarm, like Bluguard, the system can directly call u when alarm trigger, no need go thru 3rd party. U can also check the alarm status, arm/disarm thru phone call. Very convenient.

Normally, a double storey terrace alarm package is around 2k to 3k.
The performance and accuracy actually depends on how installer install the sensors. no matter what brand u buy, the sensors installer use also same, normally is ebelco brand. And the sensor sensitivity is adjustable.

So far I feel Bluguard alarm quite user friendly, easy to use. If wires and sensors installed correctly, u won't get false alarm at all.