We've all heard the amazing loud "survival whistles" made from bottle-tops or acorn caps.

I wanted to make something more ... controlled.

(you can probably work out what to do just by looking at the photo, but read on.)

Step 1: What You Need

I made this with two soda bottle caps and a piece of drinking straw, using hot-glue, my Leatherman and a drill with a twist-bit for wood (I'll warn you in advance that the hole in the caps must be drilled - if you melt the hole, the edges will be too rounded to make the whistling noise you need).

Step 2: Drilling and Ripping

Drill a hole in one of the caps, somewhat off-centre.

Inside the cap, rip out the lining of the cap from around the hole - this makes the edge of the hole thinner, and better at splitting the air.

Step 3: Gluing

Once you've ripped out the liner, glue the two lids edge-to-edge.

I used hot-glue, because the two caps had slightly wonky edges. The hot-glue filled in the gaps nicely.

Step 4: Adding the Straw

Squash a piece of drinking straw into a flat oval, and experiment with positioning it at the hole whilst blowing. It needs to blow across, yet slightly downwards.

When you have the best position figured out, tack the straw in place with a couple of drops of hot-glue, check again that the position is correct, then add more glue around the straw to hold it in place.

I also trailed a couple of strings of glue over the straw, with the idea that they would keep the straw in the correct oval shape. I don't know if they are actually needed, but they didn't damage anything...

Anyhoo, there you go - the whistle has a pleasant tone, a bit like a small train-whistle, and is not so loud that small children will run screaming from the room, or get in major trouble for playing with it in the house.

Step 5: Modifications

Randofo challenged me for a video.

I got the whistle back off my son, and made one. I also decided to modify the whistle to play more than one note.

I held the whistle on its side, noted where my index finger lay, and drilled a 3mm hole there (after moving my finger out of the way...)

The result is a nice warble, something like the small plastic ocarinas kids play at school.