The Homeland Security Advisory System is a way for the US government to help keep people in the US safe. It works by using colors to tell people how safe or unsafe it is in certain areas. The colors range from green (low risk) all the way up to red (very high risk). Each color also has a description that tells people what kind of threats might be happening in that area. For example, if the Homeland Security Advisory System says there is a yellow alert (elevated risk) then that means that there might be a terrorist attack in that area. Knowing the color helps people know how to stay safe.