I haven't created my own paging system but I've gotten quite far with Zabbix and Twilio. Zabbix's feature set includes the ability to define teams and schedules

I haven't created my own paging system but I've gotten quite far with Zabbix and Twilio. Zabbix's feature set includes the ability to define teams and schedules and execute a custom command when downtime is detected. That being said, I was happy to hear that my new work had a PagerDuty account because the fewer things I have to host and maintain the better.