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Get trained
This page explains what training agencies, standards bodies and diving medicine bodies publish. It is not a substitute for training and certification from a recognised agency, and it does not replace medical advice.
Why signalling matters
DAN's Alert Diver says being left behind by a dive boat is rare, but being separated from it is much more common. It names low visibility, currents, rough seas that hide divers from the crew, hypothermia and careless passenger tracking as contributing factors, and recommends carrying a mix of signalling devices rather than relying on one. DAN's 2010 article on currents adds that a current can make it impossible to get back to the boat. Using a signalling device, especially a delayed surface marker buoy, is a skill for training; DAN says handling the line while inflating one is tricky.
What PADI suggests carrying
PADI recommends at least two surface signalling devices, one audible and one visual, and says more adds safety. It suggests a common starter kit of a whistle plus a signal tube or delayed surface marker buoy, adding a mirror and an air horn for remote destinations. That is PADI's suggestion, not a rule, although PADI describes signal tubes as required in many areas.
Our picks by category
Surface marker buoys
PADI describes inflatable signal tubes as bright orange or yellow, rising more than a metre above the water and rolling small enough for a BCD pocket. A delayed surface marker buoy (DSMB) is similar but attached to a line and reel, and can be deployed from underwater or at the surface. DAN says a DSMB can mark a diver before surfacing but needs training, and that small SMBs can be hidden by waves.
Best for: Every diver on boat dives
Signalling devices
PADI calls the whistle the most common audible device and suggests clipping it to the BCD inflator hose. Air horns run on cylinder gas and are much louder, so PADI says a whistle is a sensible backup; DAN adds that integrated air horns add potential failure points to the BCD and need gas in the cylinder to work at the surface. PADI says signal mirrors reflect sunlight and can attract aircraft, and DAN notes they need strong direct sun and help little on overcast days or at night.
Best for: Every diver, as one audible and one visual device
Dive lights
A Scuba Diving magazine buyer's guide hosted by PADI (2020) says dive lights make night diving and wreck penetration possible, and names primary lights, compact backup lights and wide-beam video lights. It describes narrow beams of about 8 to 10 degrees for reaching into crevices, adjustable beams of about 12 to 75 degrees, and wide beams near 90 degrees for video. Most lights in that guide were rated to about 100 m, one to 150 m, with burn times from about two hours on high to about eight on low (maker ratings). Wreck penetration is a specialty with its own courses; see specialty certifications.
Best for: Night, wreck and low-visibility divers
Backup lights
The same guide names compact backup lights as their own category. Features it lists across lights include several power levels, SOS flash modes, locks against accidental switch-on and shrouds that stop the beam dazzling other divers. PADI and DAN both say lights and flashers are the most effective signals at night, and DAN notes that SOS modes help with night location.
Best for: Anyone carrying a primary light
Batteries
The 2020 buyer's guide says many lights run on rechargeable lithium-ion cells, often the 18650 size, while others take single-use lithium CR123A or C-size cells. Lights and their batteries matter for travel: DAN Europe (2016), citing the IATA Dangerous Goods Regulations, says high-intensity diving lamps must have the battery or bulb removed, or otherwise be kept from switching on, for carriage. See the travel gear guide for the battery limits DAN Europe sets out.
Personal locator beacons
DAN describes personal locator beacons as satellite SOS devices, some able to send messages, whose batteries need regular checking. Our research did not cover the registration or legal rules for beacons in each country, so this guide does not describe them.
Dive flags
The rules on dive flags differ. A US boater-education guide for Washington State says vessels restricted in manoeuvrability by diving must show a rigid blue-and-white International Code Flag A at least one metre high, and that other boats should keep well clear, preferably at least 200 feet. On the red flag with a white diagonal stripe, sources disagree: the Washington guide says it does not meet state and federal display requirements, while other sources say it is required by law or regulation in virtually every US state. Rules vary by state.
Care
PADI (2015) says all gear should be rinsed in fresh water after each dive. More on care and storage.
Sources
- Scuba Diving magazine buyer's guide to dive lights, hosted by PADI (27 March 2020)
- PADI, signalling devices
- DAN World on emergency signalling, republished by Divernet (30 May 2026)
- DAN Alert Diver, The Boat Left Without You: Now What?
- DAN Alert Diver, Diving in Currents (Mike Ange, 1 November 2010)
- DAN Europe, transporting diving lights and batteries on an airplane (Caren Liebscher, 3 October 2016)
- Boat-ed, Washington State diver-down flags study guide
- United States Power Squadrons, miscellaneous flags
- PADI blog, things that can destroy your dive gear (Danielle Schofield, 31 May 2015)