Throughout the year 2016, most of California's townspeople and animal populations have been annihilated by sightless extraterrestrial creatures , which can ruthlessly attack anything that produces noise, have hypersensitive hearing and are covered in armor which is invulnerable to any type of bullets and explosives.
'They are evolutionary perfect machines.' The idea is, if they grew up on a planet that had no humans and no light then, they don't need eyes, they can only hunt by sound. They also self-develop a medium to shield themselves from everything else- that's why they are bulletproof