A method and system of monitoring for chemical or other toxic agents includes operating a plurality of first type sensors having a first level of sensitivity to an agent in a monitored area. Concurrently a second type sensor is operated having a second level of sensitivity to the agent in the monitored area, where the second level of sensitivity is at least ten times more sensitive than the first level of sensitivity. Input from the plurality of first type sensors and the second type sensor is received and analyzed, at a central location, in order to determine the presence of the agent in the monitored area.