Every Tuesday at noon, San Francisco tests the Outdoor Warning System. A siren and announcement ring out for 15 seconds. The system got its start in the 1940s.

Reported by Julie Caine. Bay Curious is made by Olivia Allen-Price, Jessica Placzek, Paul Lancour, Ryan Levi and Suzie Racho. Additional support from Chris Hoff, Julie Caine, Ethan Lindsey, Katie McMurran and David Weir. Theme music by Pat Mesiti-Miller. Ask us a question or sign up for our newsletter at BayCurious.org. Follow Olivia Allen-Price on Twitter @oallenprice.