Introduction: Buoyancy Activated Beacon (for Lifejackets)

About: I used to be that curious kid that broke stuff by taking it apart to figure out how it worked. But I got smarter, and now I can sometimes put it all back together! My work and hobbies overlap through an intere…

Boating is a ton of fun. So fun that you lose track of time and trips often end in the dark. This is safely accomplished if you know your waters and have good navigational lighting. But there are always unknown variables that could result in an “Overboard” situation. That could be as drastic as a boating accident, or just the erratic nature of boat occupants. (Try boating with small children and pets sometime to see how that goes!)

If someone goes overboard in the dark, you want to instantly be able to locate them, as well as make them visible to any other nearby boaters. That is what this is for. It is a buoyancy-activated beacon. You can clip it onto a lifejacket, pet collar, or anything else that you want to be able to locate in the water. As long as it is hanging down from the clip, it will remain off. But as soon as it goes into the water, the buoyancy of the air trapped in the tube causes it to flip upright and automatically light up. 

Although I've thought through other fancier versions, with lots of components to 3D print and finish, that puts it out of the reach of most potential users. Instead, we are going to modify a commonly available LED glow stick. This way we don't need to worry about any of the manufacturing or sealing of components. As a result, this is an easily accessible project for almost anyone. It requires very few components and tools.


LED powered glow stick to modify. We used this one from Amazon. (This is not an affiliate link.)

Small pieces of scrap wire

Soldering iron

Aluminum tape


Small phillips screwdriver

time and patience

Step 1: Disassemble the Glow Stick

The "Nite Ize" model that we bought has a small Phillips screw that prevents the lens from being completely unscrewed from the base. Remove that screw, then unscrew the lens from the body in a counter-clockwise manner. Once you have the parts separated, remove the LED carrier and battery from the base.

Step 2: Shave Down the Base.

Carefully using a sharp knife, try to shave off as much excess plastic as is possible from the LED carrier. You want to create as much room as you can so it will easily slide up and down inside of the base unit. Every once in awhile, drop it back in the tube and see how it moves. If it does not slide back and forth easily, then keep taking down small bits of plastic until it does.

Step 3: Flip and Trim the Bottom Spring Contact

The existing glowstick relies on a spring contact being pressed up against the battery carrier when the lens is screwed down tightly. We need to remove that, trim off a bit, flip it and then resolder it back on.

Start by desoldering the base spring component from the LED leg. Then slide it out, and trim off two rings from the top. (This is because otherwise it will be too tight and you will struggle to get your battery carrier back in later on.)

Now flip it and slide that back into the base so that the newly trimmed end is facing inside to make contact with the battery unit. Test fit the battery carrier back in, and bridge across between the base and free LED leg with a screwdriver to make sure that it still lights up.

Step 4: Add a Contact Strip Inside of the Base.

Gravity is going to hold our LED unit up against the base when it inverts. So we need something conductive inside of there. Aluminum HVAC tape is your easiest method for this. Trace around the base of the LED carrier, and then cut out a small circle. Peel the protective backing, and bend it slightly so you can insert it into the bottom of the base with your screwdriver. Once you have it positioned in the bottom, press it down with something like a pen body.

Step 5: Solder Legs Onto the Bottom.

You need to create a set of contacts across the base of the LED carrier now. To create that, we will solder a short chunk of wire onto the battery spring, as well as another chunk onto the LED leg. Use short chunks of wire, and then bend them so they are similar to the ones you see in my picture.

They should not be connected together, but if you bridge across them with anything metallic you should be able to cause you're led to light. In the final product, they will rest against the aluminum tape from the previous step which will complete this circuit path.

Step 6: Test Fit Your Components Together.

The LED carrier should slide back and forth inside of the base easily. Try inverting it and seeing if it lights up. If it doesn't light up, minutely re-adjust the legs on the bottom of the LED carrier until they make contact. This might take a little bit of trial and error until that contact is made.

Step 7: Reassemble the Body and Water-test.

Thread the lens back onto the base. Then do a couple of test inversions to verify that it is not pinched, that moves easily, and that the LED is lighting up when it is supposed to. The LED might flicker a little bit whern it initially inverts, and that's alright. It is making small and intermittent contact with that tape at the bottom. As long as it consistently stays lit, small amounts of flickering from movement are not an issue.

Place it in water, to make sure it does not leak. You can see how bright it glows at in that vase in the dark while submerged.

Step 8: Usage

The point of attachment onto your lifejacket or pet collar for this will be critical to the operation. It must be submerged in order for the trapped air inside of the tube to cause it to flip. So if utilizing with a lifejacket, connect it low onto one of the lowest straps. There it will be out of the way, yet float up and flip over once in the water. If attaching for a animal, make sure it dangles from the bottom of their collar for the same reason. 

Good luck and happy boating!

Disclaimer: Remember, this is not a lifesaving device. This is just a homemade aid that could help locate something or someone it is attached to and that has gone overboard in the dark. This should not be relied upon as a life safety device, or used in place of one. The instructions in this guide do not claim to provide absolute guidance or infallibility in the manufacture of this specific or other derivative devices. Always follow your local boating laws and wear your lifejacket.

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