My furnace/heater went out a few days ago. It did this before and randomly fixed itself. I turned on the thermostat in hopes that it would do that again but now my apartment smells weird. I shut it off and closed off the gas. Windows are open. It's cold. I'll be up for a bit 
Now that you mention it, I do have one. It hasn't gone off, but I actually haven't checked its battery since I moved in. Kinda figured my landlord would have done that before I moved in. Things seem fine now (and I've slowly closed windows) but I'll check it tomorrow.

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