From available parts I had the idea to construct a purely lung automatic O2 rebreather. The 2 liter bottle guaranteed also without booster, with little pressure, a leisurely one hours dive. You have your hands free, the principle is proven thousands of times in the LARs. The rig is naturally hidden in a backpack :-). Sooner said than done ... Update / 01/2015 The backpack variant has not been so successful, especially if you want mount extra tanks.A convenient frame, a more flexible counter lung and a lockable mouthpiece was necessary. The new images are at the end, from image 33rd.