alerting

 alerting  automatically sends a message (often called a "page") to an app or site's owner or on call ops person when it's down, hitting errors, or otherwise behaving badly.

Alerts are generally triggered by monitoring when specific values change or exceed thresholds, e.g. three probe failures in a row.

Alerting is often managed by an escalation system like PagerDuty. When an ops team is responsible for an app or site, they often use an on call rotation or pager rotation which rotates primary responsibility for handling alerts between team members.