These are nice references to Motorola Pagers (mainly Motorola Advisor) using POCSAG protocol:
https://goughlui.com/2016/01/15/tech-flashback-motorola-advisor-pocsag-5121200bps-pager/
https://spectrum.ieee.org/the-consumer-electronics-hall-of-fame-motorola-advisor-pager#toggle-gdpr
http://www.hackersrussia.ru/Pagers/pagers.php
https://blog.thelifeofkenneth.com/2012/02/sniffing-pager-network-traffic-hardware.html?m=1
https://mysku.club/blog/diy/88396.html
https://github.com/unsynchronized/gr-mixalot
https://www.qsl.net/n9zia/wireless/pager/index.html
https://www.qsl.net/kb9mwr/projects/pager/plan.html
http://fringe.davesource.com/Fringe/Hacking/Phreaking/Pagers/Protocols/protocol.html
http://karbofos-zone.narod.ru/pagers-m.html
http://allpager.narod.ru/programmators/
http://jelmerbruijn.nl/pocsag-encoder/