The ExtendedAlarmOperator is derived from AlarmOperator. It has the exact same behavior, but exposes more arguments to the user to make it simpler to set advanced features of the alarm. This helps make the ordinary AlarmOperator less cluttered in the Block Diagram, while still having the option to get a more full-fledged alarm when needed.

If you need to make an alarm that exposes a different subset of the Arguments, take a look at How To Reuse Configurations With Library. After putting the object into a library, it is then possible to edit the InputOutputHint of each argument to expose it to the Block Diagram.