Hi, Marcos, So here is my take on this: It's an Edwards (brand) or equivalent buzzer mounted on a wood sounding board driven by some sort of motor or relay and picked up with a microphone in a fairly live room. A buzzer (like a bell) were common in my youth (50s and 60s) at hardware stores. Wow they are still available: https://edwards-signals.com/files/c-725_Catalog_Page.pdf More info about Edwards: https://edwards-signals.com/index.cfm?pg=21&level=50&sid=0 The basic mechanism is shown here: https://www.amazon.com/dp/B00ET6GJPG/ At the left, the contact is broken when the electromagnets attract the armature, driving the clapper into the bell. When the contacts open, the magnetic field collapses and the spring pulls the armature away from the coils. When contact is made again, the electromagnets pull the armature back. Hence the repeated buzzing or ringing. The clunking relay or motor driven cam switch was obvious at the beginning of each buzz cycle. So that is the likely source of the sound. What it means, I don't know. It is a mechanism that any electronics hobbyist of the day could have thrown together. Cheers, Richard On 2017-06-13 12:49 PM, Marcos Sueiro Bal wrote: > This is from a 1968 International Interview recording. It comes after a 1kHz tone and seems like some kind of alarm, but it is reportedly not part of any Emergency Broadcast System nor CONELRAD. It is unknown whether this sound was actually broadcast. > > http://nyprarchives.tumblr.com/post/161747409571/now-what-the-heck-is-this-sound-at-the-start-of-an > > Thanks for any help! > > Marcos Sueiro Bal > Senior Archivist, New York Public Radio > 646 829 4063 > -- Richard L. Hess email: [log in to unmask] Aurora, Ontario, Canada 647 479 2800 http://www.richardhess.com/tape/contact.htm Quality tape transfers -- even from hard-to-play tapes.