You are correct, that yelling "Fire!" will get more attention. Thank you for pointing that out.

I am not from NYC, but I hardly give a car alarm a moment's notice. If I had never heard a car alarm before, maybe, but not otherwise. Too many of them are bogus. If I heard a vocal disturbance of any kind at the same time, THAT would get my attention, though.

As for the sound of the personal alarms, some are effective, and some are a joke. Some, I think, are worse than no alarm at all, as they give a false sense of security. I have never heard any that resembled either a car alarm or fire alarm, but I wouldn't be surprised if they were available.

There are a lot of sounds out there competing for our attention, and we unconsciously "tune out" many of them. If someone wants a personal alarm, they should look for one that does not sound like the familiar, everyday sounds. It should be as loud as possible, and also as unusual, urgent-sounding and attention-getting as possible.