It's OK http://pornmd.in.net/ pornmd.com In my case, my home requires only one thermostat for a total of $250, but five smoke detectors for a total of $645 (local codes dictate that a typical 3-bedroom, single-story home requires five detectors). Plus, CO detectors have a finite life - typically requiring replacement every five to ten years because the CO detection becomes ineffective. Most CO/smoke detectors will emit a specific "chirp" when they expire. Nest has not yet mentioned this "little" fact. Perhaps they are using a new type of CO detection that doesn't wear out, but I doubt it. I suppose you could buy only one or two Nest detectors and use cheaper detectors elsewhere, but the cheaper detectors won't communicate with the Nest and you lose most of the advantages - you can't "wave" at cheaper detectors nor will they report your location. In fact, it's often not even legal to mix detectors since codes required them to be linked together so if one goes off they all go off. It will be interesting to read the legal disclaimers that accompany this product. Fire safety devices are governed by far more codes and requirements than thermostats.