Question: If an intruder has G-d forbid broken into my home on Shabbat, am I allowed to call the police? 

Answer: If the thief is still in your home, you are allowed to call the police since there is a risk of a life-threatening situation. But if the intruder, for whatever reason, has already left your home, the situation is no longer life-threatening and therefore you are not allowed to call the police.