I've had some experience with this issue as a police officer. Unfortunately, you can't just walk up to somebody's house and say "Apple says the phone is here, let me in! " Sometimes the technology works very well, sometimes it doesn't. The Fourth Amendment protects people from situations like this, and you should be glad it does.
I've had some success knocking on the door and talking to the homeowner. Especially when the parent looks at the kid and says " go get the phone, now! " More often though, people won't answer the door when I come knocking. Experience as a cop goes a long way. How you talk to people and what you tell them, plays a big part.
The accuracy of the app is often suspect. If there is one house at the end of a country road, it's pretty good. However, when you're looking at 12 apartments in one building of a huge complex, it's not nearly so good. I've seen the app say the phone was in one place and then suddenly say it was 5 miles away, when it was determined in the end that it never moved.
As far as getting a warrant goes, the officer can't swear to the accuracy of the information or the technology it's based on. Judges don't issue search warrants based on free apps. Again, you should be glad they don't. We may get to the point some day where this technology is good enough, but that's a long way off.
The question regarding the Lowjack hit is a good one. I suggest anyone wondering about that dig a little deeper. Start with learning what a Carroll stop is. The bottom line is the law is almost always lagging behind advances in technology. But you have to ask yourself how you'd feel if somebody kicked your door in and came in your house based on the information provided by a free app.
