Spoilers ahead. The end of Avengers: Infinity War was a bummer to say the least, but fear not friends, for Captain Marvel is here. In the Infinity War post-credits scene, Nick Fury took out a pager and sent a message, and Captain Marvel's colors and logo appeared on the screen as he turned to dust. How the Captain Marvel pager works in Infinity War is left unexplained, but it's obvious that whatever the pager is, it isn't standard 1990s issue. It's something more — something intergalactic.
The pager used to contact Captain Marvel is large, much bigger than the pagers used by the masses in the pre-cell phone era. Granted, it stands to reason that the pager is S.H.I.E.L.D.-made, meaning it probably has a lot of intricate tech mere mortals aren't privy to, and this sophisticated tech could explain its strange appearance. It could also explain how it functioned beyond the capabilities of regular pagers, which weren't commonly used to transfer images. Assuming the pager was made by S.H.I.E.L.D. long before the institution crumbled in Captain America: The Winter Soldier, the intricacies of how it works is probably beyond any science we in the real world can come up with. But the real question in the MCU isn't how the pager works, but what it does.
Before we get into all that, let's review everything we know about the upcoming Captain Marvel movie. The film is set for release in March of 2019, a few months before the planned release of Avengers 4. This is crucial, because it means that whatever happens in Captain Marvel will likely help set up the new superhero's role in Avengers 4. The film is confirmed to take place in the '90s, with Nick Fury and S.H.I.E.L.D. playing a part of the narrative, hence the pager. But it's not enough to say that the Captain Marvel pager is just a relic of her '90s involvement with Fury.
If the Captain Marvel pager were just any other pager, that would mean that Captain Marvel is somewhere on Earth, and has been this entire time. It seems highly unlikely that a powerful hero like her would have spent the past decade sitting on the sidelines, twiddling her thumbs while the Avengers had to defend the Earth from Loki, Ultron, and now Thanos. And, if she's not on Earth, then she's probably in space. The other thing we know about Captain Marvel is that it will be a cosmic story, taking place during an alien war between the Kree and the Skrull, two battling alien species.
In the comics, Captain Marvel gets her powers by having her DNA merged with that of a Kree, another hero known as Mar-Vell. According to Captain Marvel's official Marvel page, Mar-Vell and Captain Marvel (who was just regular CIA agent Carol Danvers when they first met) worked together and had a love affair that led to her getting her powers. Marvel Studios has already revealed that Mar-Vell will be a major character in Captain Marvel, and though the movie won't follow Carol's comic origins exactly, it's obvious that the MCU will uphold Captain Marvel's close tie to the cosmos.
This all leads to one conclusion: Captain Marvel will end with Captain Marvel leaving Earth to live in space, giving Fury a way to contact her and informing him to use it only in the case of an emergency. Because he's had other agents and superheroes to help him over the past decade, he hasn't used it, but seeing Maria Hill turn into dust must trigger his last resort. One assumes that the pager was specially made to send a signal to Captain Marvel in the cosmos. In other words: the Captain Marvel pager isn't a regular pager, it's a space pager.