Heliograph

Megaphone, MEHG uh fohn, is a hollow, cone-shaped device used to make a voice sound louder. A person speaks or shouts into the small opening at one… See more » Whistle is a device that makes a sound when air or steam is forced through it. Most whistles consist of a tube that has a hole in its side with a… See more » Siren is a device used to sound warning signals. Ambulances, fire engines, and police cars use sirens to alert traffic. Sirens called foghorns are… See more »