New cars have 3G cellular transmitters constantly sending telemetry data. This started becoming common in 2012.

https://news.ycombinator.com/item?id=37971038

4g now. 3g was turned off causing these cars to drain the battery searching for signal.

Depends on the brand still. Honda for example only does that to the top tier touring trims because it's part of their remote-remote start offering for that trim (that you have to subscribe to)