Systems and methods for suppressing the spread of fire, fire-related toxins, and other biological and chemical hazards are disclosed. One described system includes a thermostat incorporating an HVAC interface in communication with a residential HVAC system, a receiver operable to receive a signal indicating the presence of a contaminant from an environmental condition detector, and a processor in communication with the receiver and the residential HVAC system and operable to receive the signal from the receiver, and in response, send a signal to the HVAC interface to cause the residential HVAC system to be shut down.