SMBs and dSMBs will greatly aid your visability and safety whilst under or on the surface and are a requirement in many dive sites today. Some roll up small enough to fit into your BCD pocket and others are built for pure size. A dSMB, or delayed surface marker buoy, starts the dive in your pocket or on a D-Ring and is inflated underwater and sent to the surface attached to a reel. A SMB, or surface marker buoy, is inflated at the start of the dive and towed behind you so you always have a presence on the surface. Typically red in colour they come in a range of colours for different environments so it's best to get the right one for you.