Wk. 3 - Description

A loud signal makes you jump out of your seat. If you can't hear, the light will blind you if you stare into it. Though it carries no scent, it takes a certain scent of destruction to make it active. A small, simple device that can fit in the palm of your hand warns and saves lives. When it goes off, a dry taste of fear inhabits you, as you frantically rush to safety. What am I?