San Francisco residents Andy MacKinnon and Jen Liu live in the Sunset District near Ocean Beach.

From their apartment, MacKinnon says, "We can see the fog rolling in off the ocean and creeping up the street until our house is completely engulfed by fog. And shortly after that happens, we start hearing foghorns."

MacKinnon and Liu have a boatload of questions about the sounds that help vessels navigate safely through the water. They want to know:

Where are these foghorns?
How many of them are there?
Why do we still use them despite technologies like radar and GPS?
Who or what turns them on?

For those answers, hit that listen button at the top of this post, or read Foghorns: Who Presses The Play Button?