Concealing device with pull bar lock pistons

The device has a concealing fabric e.g. opaque fabric, mounted on a roller tube and driven by a drawing rod (112). An end of the rod carries a finger (33) forming a piston cooperating with a housing (43) formed in a side rail (13) guiding the end, where the finger is movable along a main axis (44) of the rod. The finger occupies a locking position, in which the finger penetrates into the housing, and a pushed-back position in which the finger is in contact with a flange of the rail and cooperates with a return unit i.e. spring (41), which brings the finger to the locking position.