A computing system performs a method of determining cumulative exposure to a gas. The computing system receives data that correspond to local concentrations of a gas from a plurality of stationary gas sensors in a home. Respective stationary gas sensors are located at respective fixed locations in respective rooms in the home. The computing system also receives data that correspond to occupancy of the home, including occupancy by a first occupant. The computing system determines a cumulative exposure of the first occupant to the gas in the home, based at least in part on the received data that correspond to local concentrations of the gas and the received data that correspond to occupancy of the home. The computing system performs and/or sends instructions to perform one or more predefined operations in accordance with the determined cumulative exposure of the first occupant.