From the dawn of civilization, people have whistled. For pleasure, for communication and for religious effect, whistles appear throughout society as instruments of pure sound. Just about anybody can make a whistle on the cheap from a wide variety of materials on hand. People have fashioned whistles through fingers and lips, through blades of grass, bits of bone and hollowed-out sticks, and finally through precisely fashioned metal tubes. You, too, can make a whistle, purely for the entertainment value, or perhaps to confront an outdoor emergency.
Cut a sheet of thin, flexible metal to about 1 inch by 2.5 inches. You can use a soda can for this. You can also fold a sheet of heavy duty aluminum foil and fold it over several times until you have a strip that is still thin enough to bend but thick enough to hold its shape when touched.
Cut the metal strip in half lengthwise, so that you have two strips of 0.5 by 2.5 inches in dimension.
Cut one of the two strips in half across, so that you get two smaller strips of 0.5 by 1.25 inches, and discard one of these two halves.
Lay the shorter strip lengthwise atop the longer strip, near the top of the strip, to make a cross shape. Leave about one-quarter inch of the top part of the longer strip sticking out.
Fold the two little “wings” formed by the shorter strip around to the back side of the longer strip, so that they grip it loosely.
Fold the little lip at the top of the longer strip down on top of the two folded wings on the back side of the long strip. At this point the smaller, folded strip should be able to slide loosely along the longer strip. Push it all the way up into the small fold you made at the end of the longer strip. These folds will become the mouthpiece.
Fold the longer metal strip into a right angle. Make the fold so that the back side of the longer strip (the side with the three small folds) is folded inward. Situate the fold just below the part of the top of the strip where all the previous folds have been made. You should have an L-shaped strip now, with all of the folded areas comprising the small part of the L, and the plain sheet of metal comprising the long part.
Press the edges of the mouthpiece so that the folds open up a little bit to give you a place to blow into. You can use a pencil, twig or another piece of metal to finagle a small opening.
Place one of your fingers across the front side of the long part of the L. Wrap it around your finger, so that the strip is almost bending back on itself in a ring. The resulting shape should closely resemble a letter P, with the folded areas of the strip forming the base of the P, and the ring area of the strip forming the curvy part of the top.
Fold the ring portion all the way back onto itself so that the ring almost closes at the point where the right-angle fold is. Leave a small gap of a few millimeters. The whistle should now exactly resemble a P except for that small gap.
Hold a finger on each side of the whistle. Your fingers will create the sides of the whistle, and, together with the ring part of the metal strip, they will form the whistle's air chamber.
Blow into the mouthpiece of the whistle. Adjust the size of the gap by moving the end of the ring portion of the whistle away from or toward the right-angle fold. When you get the gap just right, the whistle will make a surprisingly loud sound.
Add a small pebble or ball bearing into the air chamber (using your other hand) to create the characteristic warble of a coach's pea whistle.