Should parents track their teenagers phones?

I was having a conversation with a friend that has 2 kids. Her oldest just got her first smart phone (14 years old). She got the phone since she has been going to friends house after school and the mom wanted to be able to contact her at anytime if there was a emergency. I suggested she should also have the phone tracked so she can see where she is for safety reasons. To my surprise the mom acted like that was a crazy suggestion. She says she trust her daughter and doesn’t need to track her. Also it’s a invasion of privacy and how she would of hated being tracked as a teenager. I agreed that I would of hated being tracked as a teenager too.

But it’s not always about trust but safety of your child. Should parents track their teenagers phones or is this a invasion of privacy?