(Look this up)
Even though you are restricted from using deadly force in your senerio, most states allow reasonable use of force. So you don’t have to stand there watching. The chair in the room might be a usefull weapon or some other club like item. Then if he turns toward you to attack you have reasonable cause. Like I said before, look it up.
In PA you cannot protect property so if your car is being stolen it is not reasonable/lawful to shoot. However you can use resonable force like a punch to the face.