Does find my iphone track through SIM card, the phone itself, or a phone logged into the app and connected to a Wi-Fi?

Does find my iphone track through SIM card, the phone itself, or a phone logged into the app and connected to a Wi-Fi?

When you use Find My iPhone, a location request is sent to your phone. Your phone can only receive this request if it has Internet access; either through Wi-Fi or mobile data. It can't "track" it through the SIM card since it has nothing to do with that. The SIM card is only used by the phone to connect to your cell provider.

FMI uses a combination of mobile data, Wi-Fi, and GPS to figure out (triangulate) approximately where your iPhone is. It isn't always exact.

Through the GPS in the phone, more accurate when on Wi-Fi but works through data as well.