Rebreather, with a multifunctional mouthpiece with a closed circuit mode, an open circuit mode, an automatic diluent valve with an increased cracking pressure, an overpressure valve where by turning a barrel the modes can be selected and the automatic diluents valve and the overpressure valve get activated synchronously. Further said rebreather having a single piece counterlung, in which a CO2 filter cartridge is inserted through an opening and placed in between inhale and exhale side of the counterlung, to achieve a double counterlung system. Rebreather which can be transformed into a backpack, to achieve good protection and enable easy transportation of the device even in the cabin of an airplane. Rebreather with a primary and a secondary head-up display, where the primary LED based head-up display is located on the mouthpiece and the secondary, OLED or LCD based head-up display is located on the frame of the divers mask, and the primary head-up display transmits dive relevant data via an optical link, preferable infrared of visible light, to the secondary head-up display.