Blue Reef Diver Below Standard 4' Signal Tube This 4' long signal tube can be easily stored in a regular BC pocket, and is small enough that there is no reason not to bring it onevery dive. When the SMB is inflated it is long enough to be easily seen from a distance and sturdy enough to stand up to any weather conditions you may encounter. It is also conveniently labeled with "Diver Below" so you can send it up to mark your location while making a safety stop. It features an easy to use oral inflation valve with lock to prevent accidental deflation as well as an over pressure / dump valve. Our signal tubes are available in your choice of neon yellow or Hi Viz orange. Don't risk not being seen in an emergency, pick up a Diver Below SMB today.