When's the last time you changed your batteries in your home thermostat (for the ones that run on batteries). I got home yesterday to find the house very cool. After checking the fuse box I went to the thermostat to find the battery light on. I'm glad it happened now as we are leaving on a trip next week and I wouldn't want to come home to a 30 degree house.
Let me emphasize what Alix said...Check your batteries in smoke detectors....I used to be in a Volunteer Fire Dept....it is so sad to see bodies coming out of houses that a $2.00 9 Volt would have made the difference.