Solving the problem of making sound emitting paint would open up all sorts of possibilities. For paint to emit sound it must vibrate which means it could move by itself. That would make possible a paint that was attracted to light so you would only have to illuminate a wall and the paint would crawl out of the can onto the lighted area. By projecting an image on a wall, the paint could reproduce the image. This could be messy as if the sunlight fell on a painter the paint would leap after the painter and he might have to flee at high speed to avoid being painted.

If the paint could be made sensitive to electromagnetic waves, it could become a paint-on telephone applied to your ear. On the same basis, it could become an audio system and if it were painted on a large wall could reproduce really deep tones over a large area. If it could be trained to change color in response to different frequencies it could become a really huge TV screen.

Let's suppose we have paint that and changes color in the presence of smoke. Do I have to repaint the house every time I burn a pizza or slice of toast?

To Hyenuf: this is already the case if you really mess up with your pizza!

No, not really. . . My wife apparently likes to use the smoke alarm instead of the oven timer. It seems the smoke alarm is sensitive enough to go off before there is any real smoke.

Interesting concept.

I would alter it to react to specific levels of heat and/or CO in the atmosphere rather than smoke.

And connect the device to nano-circuits which lead to a small, wall-mounted speaker in order to generate a warning sound.