David - Effective 1 Jan 2011, CO detectors are required in new construction in NC. 2009 NC Residential Code R313 Carbon Monoxide Alarms. (090609 Item B-11) R313.1.1 Carbon monoxide alarms. In new construction, dwelling units shall be provided with an approved carbon monoxide alarm installed outside of each separate sleeping area in the immediate vicinity of the bedroom(s) as directed by the alarm manufacturer. R313.1.2 Where required - existing dwellings. In existing dwellings, where interior alterations, repairs, fuel-fired appliance replacements, or additions requiring a permit occurs, or where one or more sleeping rooms are added or created, carbon monoxide alarms shall be provided in accordance with Section 313.1.1. R313.1.3 Alarm requirements. The required carbon monoxide alarms shall be audible in all bedrooms over background noise levels with all intervening doors closed. Single station carbon monoxide alarms shall be listed as complying with UL 2034 and shall be installed in accordance with this code and the manufacturer's installation instructions.

You have three choices. (A)expend the effort to locate the source of this noise-i.e. rethink "risking falling thru the ceiling and disturbing...insulation" and find the #$%^ thing. (B) hire a (presumably insured)professional to do option (A). (C) "continue to let them chirp several times a day"...(and if you are lucky the source of the noise isn't some hardwired device). I would find the source one way or the other, it wouldn't be the first drywall repair for me.

I agree with Bossy. Once one starts, you might as well just do them all. It will save the time finding which one it is and the others will start going in a week anyhow. The one time I had a hell of a time finding the thing that was chirping was that there was on the floor a "water detector" and that thing had a battery that was going as well.

I don't care what Google says about the Nest microphones. There's no stinking reason a thermostat needs a mic, for Pete's sake! "Never intended to be a secret." Yeah, right. They just forgot to mention it. Oops! And the fact that I had my hand in the cookie jar doesn't mean I intended to take one. Google makes excuses for what they do. Every company does. That I get. What I don't get is why so many of Google's users make excuses for them. Well, whatever. Google's business model is raking in and selling as much information about their users as possible, full stop. You know, that, right? You don't think they're making these "free" services available just because they're nice people, do you? Don't get me wrong here, I won't say I never use Google's services. I don't use their search, but I do use their translator and maps. I'm not logged into Google when I do, but I know full well that they can identify me in other ways. It makes me a little sick to my stomach when I realize that they're building up a file of my translation and location requests. Their algorithms are digesting my queries. They know where I'm traveling in the near future, and what I'm going to do there, even though they no doubt also know that I use an ad blocker. :-) For the moment, I use translator and maps anyway. That's called informed (if reluctant) choice. So if you also know what Google is taking from you in exchange for their services, I don't see a problem. What I object to is that many people don't, because they (Google) don't post the actual privacy costs of their services in plain sight. You have to dig through the terms of service. Who does that? And by the way, though I'm singling Google out here, they're far from the only company doing this. It's happening with all smart devices, including and especially smart television sets.. Also, when they do give you software settings to reduce your "sharing," they usually make those settings hard to find and confusing to use. They sure don't advertise them. How is that right? To get back on topic with Nest stuff, as long as you realize that those gadgets sell information that can (for example) potentially tell who-knows-whom when you're away from home, using them anyway is on you. My question to you is, how often do you really think about that? As for the Nest microphones whose data "never goes to Google's servers," according to Kudzu's link -- well, that may or may not be true now. Google's record on such matters is kind of mixed. Will it still be true next year? They're not saying. But if they can think of a way to make money with those microphones, assume that they will. When they do start snarfing up the data from those mics, will they disclose what they're doing and why? You bet! It'll be right there in the terms of service you didn't read, posted in the bottom of a locked filing cabinet in a disused lavatory with a sign on the door saying ‘Beware of the Leopard.”