Trigger to update only on nesten property

I want to create a trigger on document update, but only when a nesten property is changed.
Example: Only when this property change:

"modelProperties": { 
    "property": { 
        "serialnumber": "1234" 

And i dont want the trigger to activate when any other properties under “modelProperties” or “property” changes.

How do I set up $match and $project? I have tried several options without luck, looks like as long as anything changes in the object “modelProperties” the trigger activates.

Here what this document might look like:

    "description":"Main backflow preventer",
    "modelName":"Backflow preventer",
            "location":"Room 001",
            "Close description":"test"

Any help is appreciated, thank you in advance.