I thought of this as soon as I saw the parent to your comment. I had an ex call me one time scared witless because of the siren. She was from Seattle and had never been in a severe thunderstorm with a tornado warning before.

She was in a car with a bunch of her friends who were also from Seattle. She kept asking what she should do. I kept telling her that they should pull over and seek shelter in a building. Her follow up question each time was "Is there really a tornado? What do we do if there is a tornado?"

It was really strange from my perspective, because I've done so many tornado drills the response is second nature. That being said, if there was a major earthquake I'd probably just freeze for the entire duration, and only remember to hide under a desk or in a door frame after it was over. The first time I felt an earthquake I was 23, and I didn't even realize what happened until I read about it in the news later.

It seems like one of the problems with designing an alarm for a particular level of urgency is that people react in different ways to stress. My ex was not calm under pressure, and would totally freeze up. I'm reasonably cool under pressure, but alarms will derail my train of thought even when I'm concentrating on the issue at hand. I personally think that unless the necessary course of action is extremely trivial, such as "leave the area immediately and seek shelter", constant alarms are more of a hindrance than a help. I like alarms that have a brief alert to get your attention, and then proceed to give a lower-level alert for a while, with the more pressing alert sound playing again as long as the issue is still present.

For instance, one of the the best design features I've found in my Subaru is how they handle traction control. In the Toyota's I've driven, when Traction control comes on the system starts chirping like bearing that's about to fail at 10k rpm. In my Subaru, a light flashes on the dash, just in your peripheral vision. It's definitely helpful to know TCS is being activated, but I would hardly call it an emergency.

The two times TCS seems to be activate are 1) when pulling out from a dead stop, and 2) during emergency maneuvers. In the first case, a constant alert is unnecessary. For one thing, you'll probably notice TCS has activated when it cuts the throttle. For another thing, if you can't immediately stop whatever you are doing, it's probably because you have a more pressing matter, like situation 2. I had a cab cut me off to pull a u-turn from the right last year when the roads had 14 inches of snow on them. I was about 8 car lengths from the cab, and there was a car stopped in the oncoming lane waiting to turn left. I slammed on my brakes, and realized I would never stop in time. I steered to the left and hit the gas while leaning on my horn. The cab slammed on it's brakes and I passed just in front of it. The car on the left side was about 3 car lengths past the cab, and I was already on the brakes and spinning my wheel left to avoid it. I immediately had to turn back to the left because I was pointing towards the opposite side of the intersection. I gave my car a blip of gas to straighten back out.

In this process, my traction control came on three times: once when initially slammed on the brakes (likely tied to ABS activation), once briefly when I turned back to the left to avoid the oncoming car (likely preventing me from sliding in to a frontal offside collision), and once when I tapped the brakes trying to avoid the far corner of the intersection (likely preventing me from running off the road ass-backwards.) At no point would the methodology of the Toyota be helpful in that situation. I needed to focus 100% of my concentration on the road and the two cars, not on the fact that my car was helping me not die.

On a similar note, the fact that Subaru builds a bit of slide in to their traction control is very reassuring. It gives you a lot of feeling for where the limits of the car are. I think I probably would have just ridden out the t-bone had I been in a Camry; I have no idea where the limits are on those cars because the traction control locks down and slide immediately, and the steering has all the feel of a limp-wristed handshake. Of course, a Camry is also FWD, and I had snow tires on my car, so I probably was getting some steering help from torque vectoring in the rear. I was also really grateful that my mom had taken me to empty parking lots when I was learning to drive and had me drive (and slide) around until I understood how cars lost control, and what to do.