An apparatus for indicating the presence of a threshold directional differential pressure between separated adjacent spaces includes a first conduit and an inclined second conduit containing at least one movable element that indicates a threshold pressure difference between the two spaces. The apparatus may provide a compact arrangement while allowing the movable element to have a suitable travel path length within the second conduit. The travel path may include a first stop and a second stop. An imaginary axis or plane passing through a center of a first conduit may intersect the travel path between the first stop and the second stop.