Have you ever found you self at sea, lost in a haze of fog and in need of sounding your position?
Ain't got a foghorn, but just some "common" household stuff...
Ain't got McGyvers number?

Don't worry now you two can make a useful foghorn out of crap!!! (not literally, but close)...

These are the items need.

1: Tape (i used duct tape, but any other might works as well)
2: Two "cylinders" from used toilet paper rolls. or use one from a paper towel cut in half.
(if you don't have any, just invite some friends over for some of that special chili.)
3: A balloon.
4. a bit of extra cardboard, need to be a bit wider then the cylinders diameter.
5: A scissors. (McGyver might have used a sharp rock or a sharpened paper clip).
6: A pencil.

If you use a cylinder from a paper towel, cut it in to two lager pieces and a smaller one to be used instead of the extra cardboard.

And pardon my engrish, its not my native language.

Step 1: Make a Smaller Cylinder

We need two cylinders in different sizes. so we need to make one of them just a bit smaller then the other.

1: Cut the first cylinder in a straight downwards path.
2: Roll it into a smaller cylinder.
3: Tape it..

Step 2: Cut a Small Hole.

Cut a small hole in one end of the big cylinder.
About 1 cm in diameter
(0.393700787 inch)

This will be used as the blow-hole...

Step 3: Draw an Outline

Place the cylinders on the extra piece of cardboard, and draw an outlines of both of them.

Step 4: Cut the End Piece .

1: Cut the end piece with a small distance to the outline you made in the previous step.
2: Make small cuts. The cuts need to exceed the outline a bit.
3: Bend the small newly made "tabs".

Step 5: Add the Small Cylinder.

Gently squeeze the small cylinder into the end piece and tape it firmly.

Don't be greedy with the tape. You need to make it airtight.

Step 6: Align and Assemble

1:Gently squeeze the the end piece and the small cylinder into the large cylinder.
2: Tape the cylinder. (use some smaller pieces of tape, and remember that it has to be airtight)
(The two cylinders need to be aligned very accurately to work, so place them on a flat surface while taping them.)

Step 7: Add the Ballon

1: Remove the bottom of the balloon.
2: Stretch the top part of the balloon onto the top end of the cylinders.
make sure that its stretched out tight.

Step 8: Finale Result and Test

Congratulation you now own a foghorn.

You might be able to skip the end piece step, and just make the end completely out of tape, making it more Mcgyvery. But i believe the cardboard piece makes it more durable.

Now for the testing.
Just place your mouth on the small hole and blow...

Here's how mine worked:

Note that the volume is a lot louder in real life.

Step 9: Trubleshooting

But what if the horn doesn't make any sound?

Here's what might be wrong:

1: Check that that inner cylinder is only just slightly touching the balloon.

2: Make Sure that the end piece is airtight. and that its in the right end..(same end as the blow hole)

3: Try blowing really hard.

4: Make a new one...