How Do Plano's Outdoor Warning Sirens Work?

Outdoor Warning Sirens are designed to alert people who are outside to seek shelter inside. In hazardous conditions, Plano's sirens will sound for 3 minutes. During monthly tests, Plano's sirens sound for 1 minute, followed by a voice saying "test."
Sirens are activated for:
1) Tornado warning issued by the National Weather Service
2) Trained weather spotters identify a tornado forming in or near Plano
3) Hail greater than 1.5"
4) Severe thunderstorm warning with winds greater than 70mph.
What should you do if you hear a siren? Go inside and seek more information.