Report: CO 02212019-2054A carbon monoxide alarm was received from a home in Weston. Our Central Station operator dispatched firefighters then called the home to warn residents. A homeowner answered the call indicating they did not know why the alarm was sounding. Our operator informed them of the carbon monoxide risk and asked that they evacuate the home. Upon arrival, firefighters confirmed elevated levels of the dangerous gas and traced the source to the furnace in the basement. They shut off the furnace and ventilated the home. Repairs were initiated. No injuries reported.