Surface Signaling Gear: Whistles, Mirrors and Air Horns

Whistles, signal mirrors and air horns are small devices that make a diver easier to hear or see from the surface, and each covers a gap the others leave. A whistle is the simplest sound signal, a mirror works only in sunlight and needs practice, and an air horn is louder but depends on an air supply. This guide compares them as gear to buy and carry; how and when to use any of them belongs to your training agency and instructor.

Where small signaling gear fits

Surface marker buoys and flags make a diver visible from a distance, and they are covered in our guides to SMBs, DSMBs and finger spools and dive flags and surface floats. Whistles, mirrors and horns are different. They are small, light and cheap, and they work by sound or reflected light rather than by being tall and bright. Kits that bundle several items are covered in our save-a-dive kit guide.

DAN's articles on divers separated from their boat describe visible signaling gear as potentially decisive and recommend carrying several kinds, because no single device works in every situation. They also stress maintaining your equipment and practicing with it. This post sticks to the gear side of that advice. Training in how to use these devices, and when, is for an instructor or your training agency. Our stocking stuffer list leaves signaling gear out of its list.

Whistles

DAN describes audible signals as carrying farther than a voice, and calls the whistle the simplest of them. As gear, whistles are inexpensive and have no moving parts to fail. What you are choosing between is mostly construction and how you attach it: plastic or metal, the shape of the mouthpiece, a loop or lanyard, and a spot on your BCD where you can reach it.

A whistle has limits. DAN's account of a group left at sea describes one blown hard that did not carry to a boat upwind in the breeze, which is a reminder that sound depends on wind and distance. That is a reason to treat a whistle as one tool in a set rather than the whole plan.

Check that its attachment cord will not catch on other equipment. The maker's page or your BCD's manual will say what attachment points the BCD has, so use those rather than improvising.

Signal mirrors

According to DAN, signal mirrors are small and inexpensive and can be seen from long distances, but they only work in sunlight and take practice to aim. The same article notes that an account of a lost group suggested a mirror might have attracted a passing boat much sooner. As gear, what matters is toughness, whether it floats, a lanyard or loop, and whether it has an aiming aid.

If you are considering a mirror, plan to ask an instructor or training agency about practice, since aiming is a skill. A mirror does nothing in cloud, rain or darkness, so think of it as a daytime device. Check the maker's page for what a mirror is made of and whether it is meant for marine use.

Air horns

DAN describes an air horn as more powerful than a whistle, with one drawback: it stops working when the cylinder is empty. Most diver horns connect to the BCD's low-pressure inflator hose, so they depend on the BCD, the hose fitting and a supply of air. For a buyer, that raises compatibility questions that a whistle does not. Check the horn maker's page for which inflator connectors and BCD makes it supports, and check your BCD's manual before adding anything to the inflator.

Because it connects to part of your life-support equipment, an air horn is not a casual add-on. Ask your dive shop or the BCD's maker whether it is compatible with your model and how it should be fitted, and have a technician fit it if they advise that. Do not alter fittings or hoses yourself.

Comparing the three

Our dive light guide covers lights, which DAN lists as another useful signaling tool when daylight fades.

Buying, carrying and maintaining

Buy devices made for diving, because they are built to handle salt water and rough treatment. Check how each one attaches and whether it adds clutter to your BCD, since loose cords snag. Rinse them after use, as you would the rest of your gear, and check them before each trip. DAN stresses maintenance and practice with signaling equipment, and a whistle with a cracked body or a mirror with a worn lanyard should be replaced.

When you compare listings, read the description for the material, the cord and any statement about marine use. Be skeptical of claims about range or loudness that come without a source, because a figure on a listing is not the same as how a device performs on the water. Inexpensive items like these are usually worth buying new, so there is little reason to take a chance on a cracked or corroded second-hand one.

Signaling gear does not replace training, a buddy, an operator's procedures or a surface marker. How you carry and use it, and what your boat or site requires, should come from your instructor, your training agency and the operator. If you are buying for someone else, ask what they already carry.