A gas detector including a planar mirror; a concave spherical mirror facing the planar mirror, having an optical axis orthogonal to the planar mirror, the distance between the planar and spherical being equal to 0. The invention further relates to a corresponding communication system as well as to a sender and a receiver for use therein. The device includes a first valve member arranged to permit or interrupt communication between the chamber and the pressure fluid source through the second branch upstream of the chamber. If the current liquid level is determined to have surpassed the high liquid level mark, the method and system may activate a mechanical shaker that produces vibrations to physically shake the pump. This results in a robust, reliable connection of two flexible printed circuits. The light returned from the specimen is received by the distal end of the fiber-optic component and transmitted back and out the proximal end of the fiber-optic component.