How to generate alerts on the combination of values of 2 properties.

Make a service that will check values of both properties and if both of them are above threshold , return true which you can be saved on another  Boolean property .

Generate an alert when this Boolean property is true.

Let me know if you find this useful.

You can create a subscription to value change on one of the properties or both, and there check the threshold, once detected the alert you can throw it by hand through a service, or build you own alerts system.