Not to be confused with Apple’s latest revolutionary I/O technology, these towers stand as remnants of an era in which Civil Defense authorities used these structures to sound off a siren for one of two signals: attack or alert. West Covina looks to have 3 of these Thunderbolt sirens still standing. Although it doesn’t look like any power is going to them, it is cool to have a small, yet so significant, piece of history so close.