It's easy to buy hardware to attach to a lanyard that will break away if snagged accidentally. My work requires that I wear an ID badge around my neck, and my employer supplies simple neck lanyards with plastic break-away clasps.
That's OK...I guess. I'd much prefer a solution that is cord only, using a break-away knot. A search of the internet didn't yield exactly what I was searching for, so I tried my own design.
Here's how I did it.
Step 1: Start With About 60 Inches of Cord.
I used 1/8-inch diameter cord, similar to paracord, but a bit more stiff. Paracord would probably work even better.
Step 2: Make a Bight 24 Inches From One End.
The length of the bight is not critical. After experimenting, 24 inches seemed a good way to start, but the knots will need dressing, and exact lengths will be adjusted later.
Also, the diameter, and the stiffness, of the cord you choose to use will affect cord length. Be prepared to be flexible and innovative!
Step 3: Tie a Decorative Knot.
Tie the knot about 1-3/4 inches from the bight. Dress the knot, leaving one cord of the bight short, about 17-1/2 inches long. When the length of the loop and short cord are about right, tighten up the decorative knot.
I chose to tie a Diamond Knot (Boatswain's Whistle Knot). Stormdrane recommends this page to help learn the Diamond Knot.
Any decorative knot will work. The Celtic Button Knot is another favorite of mine. Tie it along a single strand of cord and feed the bight back through, following the original strand back out, to form a loop.
However, the Diamond Knot is much simpler, and makes a smaller, more compact knot than the doubled Celtic Button Knot.
These dimensions were designed to fit a split ring with a diameter of 1-3/8". If you'll be attaching the lanyard loop to a ring of a different size, adjust the loop length as needed.
Step 4: Finish Each End.
The longer leg of the lanyard should be about 30 inches long. Fuse the ends with a flame, if the cord is synthetic, to prevent unraveling and fraying. The end of the shorter leg of the lanyard should be as smooth and narrow as possible. This will be the cord that will slip out of the break-away knot. If the end of the short leg of the lanyard is too large, it won't slip out of the knot.
Step 5: Tie the Break-Away Knot.
To tie the Break-away Lanyard Knot, follow these steps:
First, tie a simple Overhand Knot at the end of the longer leg. Dress the knot tightly at the very end of the cord. This will help to prevent the end of the knot from slipping under tension.
I used a Common Whipping Knot as my Break-away Knot. Using the longer leg of the lanyard, I tied a whipping knot on the shorter leg. The longer the whipping, the more friction will hold the shorter cord, and the harder it will to break away if snagged. You'll need to experiment with different lengths of whipping and different degrees of tightness with which you cinch the knot.
Second, make a bight in the longer leg, at the same length as the shorter leg.
Third, lay the bight over the shorter leg.
Fourth, wrap the longer leg around the bight and the shorter cord, wrapping it around three cords all together. Wrap towards the bight, until you reach the end knot, and insert the knotted end of the long leg into the bight.
Fifth, pull on the longer cord to slowly tighten the knot. The tighter you pull the knot, the more load will be required to "break-away". You may have to repeatedly tie the knot and experiment with pulling the lanyard off your neck.
The goal is to have a lanyard that fits comfortably around your neck and holds your badge or whistle securely, yet if the lanyard snags on something, or a perpetrator attempts to choke you with it, the knot will break away.
Tighten the knot and then try to pull the shorter cord through the knot. If it seems to pull too easily, tighten the knot more.
When you have the knot tightened sufficiently, pull the shorter cord until its end is right at the edge of the knot.
Step 6: There You Have It!
A neck lanyard secure enough to hold an ID badge or whistle or compass, but safe enough to break away if snagged or caught.