Apple Watch in find my

I miss placed my watch about a week ago. Location service were turn on and the last location shows up in find my. I went to the store and a couple of other places and the watch updated to those locations. Currently it shows it was at a restaurant I was at last night. Only place it could be is in my car that went to all those locations but I have searched high and low in my car. Just wondering how it’s connecting and updating my watch to those location because the batter would be dead. I try to play a sound and nothing happens I also put my watch in lost mode and it still says pending. It’s a cellular version with a active data plan. Just trying to get a better understanding of how it’s working and what exactly is making it up trate every few hours to my currently location.