Ask HN: How do GPS tracking devices send signal

I am looking for a GPS tracking device (a device that tracks the position of my car, kid or bike).

With the [help of HN](https://news.ycombinator.com/item?id=41486352) I realized that all GPS tracking devices require a sim card or some form of monthly subscription. You need to pay to send the GPS data to the satellite.

However, a user recommended using an old phone, and I believe even without a sim card, a phone will send GPS data.

There is clearly a whole in my understanding somewhere. Can anyone enlighten me on 1) a GPS tracker that does not require monthly subscription, or 2) explain to me why phones can do it?