How does a tornado alarm work?

Question

Well I know that they warn us when a tornado is on the way, and I live in Texas where Tornados come every year in April-June. But what interests me in the first place is how do they even work? How do they know when to sound off? I have one like right down the street from my house and I've never like really studied it before. How does a tornado alarm work?

Answer 1

Once the National Weather Service issues a tornado warning the city sounds the alarms/sirens.  I grew up in tornado alley and got used to hearing them atleast once a week.

They also use the sirens for other weather warnings and civil defense reasons.  The website below goes into more technical details about how the sirens actually work.

Answer 2

City officials turn on the sirens.  In our town sometimes they don't turn on the sirens even though the national weather service has issued a tornado warning.  They think they know better when to sound them.