A device for indicating the flow of gases includes a vertically extending conduit section in which is disposed a ball. The ball seats on a lower seat at zero or minimum gas flow, and on an upper seat at maximum sensed gas flow. The upper seat is configured to permit essentially unrestricted gas flow when the ball is seated on it.Electrical means are associated with either the bottom seat and/or the top seat and co-acts with the ball to sense either minimum gas flow or maximum gas flow, and generate a signal responsive thereto.