When should I replace the batteries in my Honeywell thermostat?

Install fresh AAA alkaline batteries immediately when the LO BATT warning begins flashing, which occurs about 30 days before batteries are depleted. Even if the warning doesn't appear, you should replace batteries once a year or before leaving home for more than a month. To replace them, pull the thermostat from the wallplate and insert 3 fresh AAA alkaline batteries (page 20).