Its not quite law here in NZ, but it might as well be, I know with the local council, any work you get done on the house, the permit wont get signed off when work has been completed unless enough smoke detectors are installed in the house.

We discovered this when we added to an un-attached garage and they would sign it off unless we added another smoke detector in the front of the house.
We couldnt understand why he want to check the house when the garage was out the back….

cheers