The reason you cannot find a working free version of this is not that the tool is hidden — it is that the capability as described does not exist without breaking the law somewhere in the chain. Carriers will not hand live location to a bare number, and phones do not broadcast their position to strangers.
What actually happens when you search for it: you land on a data-broker site selling a reverse lookup (name, carrier, maybe a city), or on a form that asks for a card number before showing you an "approximate" map that resolves to the wrong country. Both are the same business model — sell the hope, deliver a public record.
Covert tracking of another adult is also a legal minefield. In the US, the federal Wiretap Act and state stalking statutes cover it; in the UK, the Computer Misuse Act and the Protection from Harassment Act; across the EU, GDPR plus national criminal codes. "I suspected cheating" is not a defence that survives contact with a prosecutor, and evidence gathered that way is frequently inadmissible in the divorce proceeding it was collected for.
The transparent alternative for a family you are responsible for is a monitoring app installed openly on a device you own. Ultimate Phone Spy covers Android, Windows and Mac — location history, geofences, message and call logs in one dashboard (parental control features). The child knows it is there, which is the whole point: oversight, not surveillance.
If the person is an adult partner, the options that hold up are a shared sharing agreement (Find My, Google Maps, Life360) that both parties opt into, or a professional — a lawyer or a licensed investigator — telling you what is actually admissible.