I know there are other threads about about these but and there are a million different options but I'm in the market for something.

Needs to be mobile. Home, office, trips, etc. I want it to alert me via an app or some type of alarm if they go out of range

I don't want a tracking/e-collar. I already have an e-collar that I like.

What are the differences in the Halo system and the Whistle or FIT collars?

Lastly, I don't care about cost. I'd gladly pay whatever one of these things costs to have Lucy back. I don't want to make the same mistake with this new pup