My mobile carrier offers access to an API that can send SMS to its users. With systemd’s timers, I have been able to make a script that warns me when the load on my server is too high!
Basically, timers work by stating a service repeatedly; which in turn starts a script in this case.
This shell script is responsible for checking the load and sending a SMS. Of course, you can have it send you a mail too. Or tweet it, or whatever - sky’s the limit.
This shell script is in charge of checking the load average and sending a SMS if it’s too high.