Adding a new type of alert condition would be done in the Server code, which lives in the ${rhq-trunk}/modules/server/jar module. You can start out by looking at the org.rhq.enterprise.server.measurement.CallTimeDataManagerBean SLSB, which contains the methods that are called to add, query, and purge call-time data. I'm not super familiar with the impl of the alerting subsystem, but one place to start would be the org.rhq.enterprise.server.alert.engine.AlertConditionCacheManagerBean SLSB. As you can see, that class has a checkConditions() method for each different type of alert condition. You should be able to look at one of the existing methods and see what it does and when it is called.

Good luck,
Ian

Frank,

I'm working on putting a document together that will list in detail all the various places in the code base that need to be modified to extend alerts in this way. Stay tuned.

-joseph

FYI, alerting on call-time data is available in the RHQ 3.0.0 community release.  It's considered an experimental feature, however, so you will need to go to the administration page an enable the experimental features option to use it.  Much thanks to Frank for this contribution.