Scuba Octos
Your Scuba Octo is your backup (or safe second) breathing apparatus. These usually have the same components of your regulator and most of them feature the same benefits and characteristics as their regulator counterpart. There are typically two styles: 1) an octo that is connected to your first stage with a hose or 2) an integrated Octo/Inflator on your BCD. With benefits and drawbacks to both, you decide which style you prefer.