I've tried with my own and friend's cars. Pretty much all of them use one time keys, so the only way to actually open a car is to intercept a signal that the car does not receive, then play it back. Might be some other encryption stuff too because I could never get it to work.

It has some useful universal remotes so you can mess with with public tvs and other stuff. What it really boils down to is it's a very nifty tool that can do a lot if you know exactly what you're trying to do. What frequency the thing you want to mess with operates on, what kind of signals make it do things, etc.

I think you're talking about a relay attack and the Flipper Zero cannot do that.