This was my first Amber Alert on my smartphone and frankly I found quite annoying. My iPhone squeeled loudly and vibrated waking my sleeping girlfriend. I understand two kids may be in trouble but this seems like a very inefficient use of a very large number of people's time. We were lying in bed reading and sleeping nowhere near any cars. The signs on the highway seem completely reasonable.
Did they really send it to every modern smartphone in California? Are we expected to be on call for the police/government at 11pm?
I eventually figured out how to turn it off on an iPhone[1]. The first few results on Google were non-responsive - apparently being DDOSed by the Amber Alert!