Try making a rain detector that will set off an alarm when it starts to rain.

--> See the flash animation

You will need
a) a plastic bottle or tube,
b) sticky tape,
c) glue,
d) sugar cubes; and
e) some marbles.

Steps

1. Rest a tray or a board on a brick to make a slope.

2. Glue a row of sugar lumps near the top of the board. ( Or you could try small heaps of salt if you want the experiment to work fast.)

3. Put some marbles in the container, seal the end with sticky tape and rest it on the sugar lumps.

4. When it rains, the sugar cubes will dissolve in the water and the container will roll noisily down the slope.