The biggest concern in these environments isn't information reaching the people inside - it's those people extricating that information (intentionally or otherwise). So having a system where e.g. some scientist's family can tell them they need to call right away is super helpful and not a huge security risk because they have to go through the process of leaving before they can actually contact them. There's no [obvious] way to MITM the pager and get it to extricate any data.

"The T5 supports message encryption using the industry standard AES?128* encryption algorithm. Each device is programmed with a unique key. Messages are encrypted as they enter the Spok network and are sent over the air to the device where they are decrypted for display to the user."

https://pagersdirect.net/collections/alpha-numeric-pagers/pr...

However, there seem to be other weaker links in that chain (like the email that's being sent to the host).

You might be interested in the 9/11 pager intercepts (https://911.wikileaks.org/)

The encryption isn't too much of an issue, you're usually just paging a phone number or a code like '911' from your family who otherwise have no other way to reach you.