I have almost hit several emergency vehicles during the day due to my car's sound dampening and my car stereo (which doesn't have to be loud to block out sirens). At night, this has never happened because I have never not seen the seizure-inducing lights. My sample size may be less than a hundred, but you're making an assumption that piercing sirens at night are the most effective way to alert the public of an emergency. And for those blind pedestrians, low-frequency (or even lower decibel) sirens are more than sufficient.

I live on the 9th floor of a condo building that unfortunately has single-pane windows. If I don't have an extremely loud fan blowing, I will be woken up by everything from emergency vehicles to motorcyclists. I realize this comes with the territory of living in a city, but if cosmopolitan cities like Geneva can incorporate effective noise pollution laws* then there's room to improve.

* http://www.cagi.ch/en/logement/bruit-de-voisinage.php