Is it possible to track person location without them knowing?

I’m getting a bit worried about my teenager’s whereabouts when they’re out with friends, and I want to make sure they’re safe without being too intrusive - is there a way to discreetly monitor their location, maybe through their phone or some other device? I’ve heard of some apps that can do this, but I’m not sure if they’re legit or if they’d even work without them knowing.

Many apps claim to track without a user knowing, but most require their consent or installation. Discretion often isn’t guaranteed and can backfire ethically and legally.