Abstract: A switch assembly for sensing velocity of airflow along an airflow path and having a vane for disposition in the airflow. The vane is pivoted in a case of framework and rotational movement of the vane about the pivot axis actuates a magnetic reed switch mounted within the framework. A variety of weights are provided for attachment to the side of the vane opposite the side upon which the airflow impinges for providing a variety of unbalance torques to the vane which are counter to torque produced by airflow impingement. A consequent variety of airflow velocity switching points may be obtained. For airflow paths which are small in cross section, the pivot axis of the vane may extend parallel to the cross section and the angle through which the vane may move approaches 80.degree. from the plane of the cross section so that a minimal surface of the vane will oppose airflow through the path.