You can create API monitors from test cases created in SoapUI or SoapUI NG (part of ReadyAPI). The monitors will run from AlertSite global locations and your private nodes and will check your API availability and response time.
API Monitoring Tutorial
SoapUI and ReadyAPI Project Requirements for AlertSite
Create API Monitor From SoapUI Test
SoapUI API Monitor Settings
Configuring a Timeout for Your SoapUI Monitor
SoapUI and ReadyAPI Integration
MonitorsAPI Endpoint Monitors