Here in NJ CO detectors are required, and have been for a few years. Policy that I know of is to 'follow mfg instructions'.
We have a two page 'official' paper, but...it's not written well.
Basically, IF there is a fuel burning appliance, a CO detector is required. One on each level (floor) where there are sleeping rooms. Battery and 'plug-in' types are allowed, as are combo units.
I'll get a copy of the official paper Monday, and if I have time, transcribe it here.
John
