An Octopus is another name for an alternate air source and has the same properties as a second stage with the only difference that the purge button is yellow and the hose is longer. An Octopus used in an emergency situation and should therefore be reliable and in a stressful situation deliver the desired amount of air. Choose your alternate air source carefully. If you are unsure about your choice, please contact Alpha Diving for expert assistance - We are ready to help you.