You could probably use the Nest app to remotely turn it back on.
Re:Nest introduces their Smoke Detector
by devindotcom on Tuesday October 08, 2013 @04:24PM
(#6517595)
I think you'd want to know right away that you have a CO leak. You can call in an emergency utilities guy to drain the pipes - the internal insulated ones won't burst within a couple hours. And as the other commenter says, you can almost certainly restart the furnace or cancel this action.
"If Nest Protect’s carbon monoxide alarm goes off, your Nest Thermostat automatically turns off your gas furnace"
In a winter vacation scenario this could be disastrous. Nest decides to turn off the furnace, but the homeowner is away and unreachable. It doesn't take long for the temperature to plummet, causing water to freeze and burst pipes.