I had some fun wiring one of these up for my apartment to check air quality. Relatively inexpensive, although calibration is an issue, and I'm not sure I'd trust it in an emergency.
Personally my preference is towards consumer products where possible, because they require less effort and look more presentable... Especially when its for a non-technical user. For instance, the smoke detector is a First Alert. It appears First Alert does have a natural gas detector, but it doesn't appear they make it with support for their Onelink protocol.
