Small Details In 'A Quiet Place' Reveal Secrets About The Apocalyptic World

The cross memorial the family erected for the child who dies at the beginning of the film features photos screwed onto the wood rather than nailed, because using a hammer would have been too loud. 

In the first scene, you can clearly see that the grocery shelves in the pharmacy have been cleared out except for bags of potato chips and other noisy foods - another result of living in a world with super-hearing monsters. 

According to the calendar seen in the film, October 3 is day 473 of the alien invasion, meaning it began on June 17 of the previous year, roughly a couple of weeks before the Fourth of July. This would explain why there are fireworks in the family's fields. 

The warning system using the red lights not only informs of danger, but it emits a high-pitch frequency when turned on that can distract the creatures. 

In the dinner scene toward the beginning of the movie, the family eats with their hands to avoid the clatter and scraping of silverware.

As pointed out by Reddit user u/bikogiidee, the newspaper clippings seen near the beginning of the film create a complete timeline of the monsters' invasion of and eventual dominance over Earth. They write:

After examining the news articles closely, a magnetic pulse crippled Wall Street and erased hard drives. This suggests a negative, potentially global financial impact. Also, highrise buildings lost elevators and running water. These events occurred on May 12, 2017.

There is no date for the meteor impact with the "force of a nuclear bomb" in Mexico that injured 2,500 people. Another article confirmed 128 separate alien invasion landings (no date). If each landing had the force of a nuclear bomb, then it was likely complete chaos and carnage around the world as first responders and bystanders were wiped out by aliens.

The military were defeated on Nov 7, 2018 as alien armor is impenetrable. The US President prayed and newscasts ended on Nov 15, 2018. If the first magnetic pulse article (2017) is related to the alien invasion, this suggests it took the aliens 1.5 years to conquer world governments.

Other events include a massive death toll in the hundreds of thousands in Shanghai, China, reported on Nov 27, 2018. The "They can hear you" headline posted on Nov 23, 2018 - after the devastating military defeat. Lastly, another article announced that world powers united to attempt to defend Earth.