We use a fairly simple method that is easy to implement - heartbeat monitors. For each system that CPS runs jobs on, we also set up an hourly CPS job called HEARTBEAT for that system that executes on the top of the hour. It can run a simple ABAP report like RSUSR000, or if the system is a non-ABAP environment it can create a flag file via a Redwood agent, for example.
An ordinary (SM36) SAP batch job (or script run via cron in my other example), is then scheduled to run hourly on the half hour. In an ABAP environment the job runs a report that checks table TBTCO to see If a job named HEARTBEAT has been executed by the CPS user in the last 45 mins. If it can't find a job, it assumes that there is a problem with CPS and sends an SMTP email to our support staff to check the issue. In my other non-ABAP example a shell script could check the the flag file created by the HEARTBEAT job is less than an hour old, and send an SMTP email if it is older than an hour.
If you don't have a 24x7 team that would pick up these alert emails, you can always use an app like Boxcar on your iOS device. It has ab email address associated with it that makes the app sound a loud alert if s message is sent to that address. You then use that address in your SMTP alerts.