Ever since the linked clip was posted, when this time of year comes round I think about the people in that video and the sound of all of those PASS devices going off.
Current BBC news coverage: September 11: America remembers lives lost in al-Qaeda attacks
PASS Devices: Wikipedia
Dr Mark Heath: CNN Transcript
I accept that this might not be the right community to share this.
It’s a sound that permeates much of the post-collapse footage; when a much younger and less experienced me first heard it, I thought it was car alarms - I didn’t connect it with the fate of hundreds of fire crew.
Here’s another clip that captures the “chirping”.