Source: http://jalopnik.com/the-ten-weirdest-saf...

Pedestrian airbags activate within 60 milliseconds of the front bumper’s pressure tube sensing a person, as long as the SUV’s moving between 15 and 30 MPH. The air bag pops out right ahead of where the windshield meets the hood and keeps a low profile, so you can see out as you move on to your next victim.