Is there a way to have an alert that notifies me when any stocks meets a condition: for example price crossing above the moving average 9 or moving average 3 crossing above moving average 9.

You can create a Condition.

Creating Scan and Sort Conditions
Personal Criteria Formula Conditions

And use it as an EasyScan Condition.

EasyScan Basics
EasyScan Expanded

And you can even use an EasyScan as the basis of an Alert to combine Conditions, but Alerts can only be created for individual symbols, not for entire WatchLists.

Setting Alerts
Monitoring Alerts