(Jashrema had some insight on this from Sierah's case, iirc?)
The way it was explained to us was when Sierah went missing, her phone pinged off a tower maybe a couple miles away, across the state line in Michigan (she was close to state line) BUT
pinging only works to the tower, if one tower can't "accept" the ping (because of usage capabilities) it will ping to the next closest tower. In Sierah's case, there were 3 towers in range of her signal and the pinging triangulated between those towers. those towers represented a 10 mile radius which is a huge area. Her killers phone also pinged at the same tower for over 2 hours after she went missing. this caused people to think..Oh my gosh..he was in the cornfield for 2 hours with her! Not necessarily so, his home was 5 miles away. He took her there. His phone could have still been pinging off a tower 5 miles away..see?
To actually FIND the exact location of the phone, the GPS on the phone has to be ON. Then, you can go into a person's ICLOUD acct. and "Find my phone". That will give you the gps coordinates of the phone. On an android, it will also do so. But it has to be "ON".
Many people do not turn on the GPS to be running constantly as it drains your battery a lot quicker, so those features are off. Or say, you don't know the persons icloud login info...LE can still get it but it's much more trouble and precious time is wasted.
So in the girls case, if the phone was pinging around town, it COULD mean that those were the towers that were being used just to give cell access to make a call. Like if they were in the woods, a cell tower isn't probably right there, but maybe a couple miles away...that's where the phone would ping. If that tower was at full usage capacity, it would ping off another tower, maybe that tower is 5 miles away, and sometimes you are just completely out of range of ANY tower and then you have no service.
So the pinging of the phone "in town" doesn't necessarily mean that the killer had the phone and was walking around town with it.
It would be useful to know whether or not they recovered their phones or not.
I always have gps on cuz I don't give a d*** about the battery and I make my kids have theirs on too. There are also apps you can download, have them open and running that continuously update your location up to a few feet that you can access from your laptop. So if your child had that app on their phone, you could go to your computer, login, and see exactly where their phone is located.
Pinging just doesn't say that much really.