A few days ago, while on my morning run, I passed a condo development just as all its fire alarms went off. (With several civilians outside wearing orange safety vests, it was apparently a planned drill.)
I heard the alarms even through the earbuds connecting me to my iPod, which was probably turned up louder than I should. I found this to be a great indication that the alarm’s design was sufficient to alert the residents, since I heard it from across the street and over the music.
But when I removed the earbuds, I could tell that there was more than one distinct alarm sound. This is troubling, because I heard at least three different sounds, and since I heard only one of them, the other two are far less effective at getting peoples attention, yet are being relied upon to alert a good number of people (easily several hundred, and perhaps closer to a thousand than 500) of imminent danger.
The one sound I heard is the one that has been demonstrated to be most effective for the widest range of cases–young kids sleeping, older adults with hearing loss, and those of us in the middle. This is, of course, the Temporal 3 pattern (T3), with a ~450 Hz square wave tone, rich with lots of harmonics that make it an annoying, attention-getting sound that easily overcomes other ambient noises.
It was hard to discern the precise details of the other alarms used in the condo complexes, but they were both higher in pitch–probably higher enough that they fell in the typical hearing loss frequency range–and seeming consisting of a sine wave, missing all the sharp overtones that make a square wave sound better at alerting people.
While it may be possible that these other two alarm sounds exist in this development because they are provided by a different model alarm, it’s just as likely that all these alarms are similar models, and that some simply have their configuration jumpers set to produce different tones.
And I won’t even go into the separate issue of different sounds being used for the same purpose confusing people who aren’t aware that they all have the same meaning.
It may sound silly to harp on small details like high vs. low frequencies and sine vs. square waves, but time and time again, it has been shown that not paying enough attention to such things kills people.