The speed at which airbags deploy is mind blowing. In the video, the steering wheel air bag starts deploying around 20 ms after impact.
that's the standard for all airbags
The mechanical part (rapid inflation) is more interesting, but for a long time, they did it the "obvious" way: a precisely-calibrated explosive charge, just enough to fill the bag without tearing it apart. Now, I think they're moving toward compressed air, which probably requires some clever engineering to build a sufficiently responsive electronically-controlled valve.
False-positive airbag deployments are not viewed very positively by the affected user (even if its strictly better than a single false negative)
So a false positive seems strictly worse than a false negative to me.