When Douglas Aircraft was operating the entire Camp NorthEnd site in the 1950s as a backup production facility for nuclear missiles (luckily, no nuclear fuel was ever present here), Cold War-fueled fears were dialed up to11. So in 1952, this loudspeaker was one installed as part of an air-raid alert system. During the Cold War, standard signals were used throughout the country for civil defense purposes, referred to as "alert" and"attack." You'd recognize the "attack" tone, meant to warn of imminent enemy attack, as that wavering (rising-falling) siren sound frequently heard in war movies during an air raid or nuclear attack.
But don’t be alarmed. Thankfully, we don’t need air-raid sirens anymore.