How come, the "Find My Phone" app on my laptop can locate the position of my iPhone in my house, down to what corner of a room it is in, despite the layers of wood framing, sheathing & the steel roof (and the trees above - I live in the woods), but my dedicated outdoor GPS devices struggle or fail outside with just a forest leaf canopy? (There is no cell service where I live, so triangulation by cell towers is not a factor).

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Steve Boal

Most of the world's political, social, and environmental problems have the same root cause: human overpopulation. By 2050 or so, the world population is expected to reach nine billion.

As I understand it, "Find My Phone/Device/iPad/AirTag/Tile/etc..." tracking services use Bluetooth, not GPS. They rely on having one or more Bluetooth enabled devices nearby (in this case your laptop, but really anyone's device) to communicate with and locate your lost item. If there were no Bluetooth enabled devices within range of your lost item then you'd never find it.

I have earthmate downloaded on my Samsung. It is the mapping program associated with my inreach. In the middle of nowhere, where there is no possibility of wifi, bluetooth or any form of electronic communication, the Earthmate app still works, showing and tracking my location and route. I can only conclude the following:
1. My cell phone has satellite capabilities built into it
2. My cell phone is magic.

Bluetooth is not required for tracking. When my wife recently traveled from NY to Texas to care for grandchildren when our son was away in a training program, she took only her iphone, which I could track from home on my FINDMY app. I could follow her progress to our local airport an hour away. Of course she had it turned off during flight, but after landing I could track her exact location from the time she rented a car at the airport until she arrived at our son's house over an hour away in confusing traffic. She had only the iphone with her, no other device with bluetooth or anything else.

Closer to home I often travel to and spend time working at our lake camp before she comes later from home. It is easy to follow her route when she decides to get on the road only with her iphone. By the way, she can also track the location of my iphone and/or my mac laptop whenever she wiishes.

I use the topos on my Iphone while hiking in areas with no cell service.

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Old canoeists never die---they just smell that way.

Bluetooth is the only way to track some devices such as AirTag or Tile trackers. Bluetooth is just one of many ways to determine the location of a smartphone, GPS and triangulation via cell towers or known wifi networks are other methods. I can't comment on what location services were used to track your wife's journey or your location at the lake camp as I don't know all the details, it may be a combination of any of these services. My initial reply addressed the question of how a device can be located using the "Find My" app in an area where there is no cell service and GPS fails.

All that I have read indicates that the the "Find My" app uses Bluetooth. The link below has more details on how it works.

https://www.pocket-lint.com/phones/news/apple/149146-how-to-find-a-lost-iphone-ipad-apple-watch-airpods-or-mac/

From that site: "How does the Find My app work? Apple's Find My network and app is a crowdsourced network. It uses the hundreds of millions of Apple devices that use Bluetooth wireless technology to detect missing devices or items nearby, and report their approximate location back to the owner."

I too use my smartphone for location tracking while using offline maps while out of cell range. But that's a different use of location services than the original question. The original question was about using a device to locate another device - in this case, using a laptop to locate a lost iPhone. Your use case involves a cellphone locating itself, not another device.

A smartphone can locate itself in the wild without wifi, bluetooth, or cell service because nearly all smartphones have a GPS receiver. A GPS receiver is passive, meaning it can only receive information from satellites about the phone's location, not transmit anything such as emergency messages.

Interestingly, communication capabilities between phones and satellites are changing, from one-way passive receivers to two-way receivers and transmitters. Apple's iPhone 14 (and the new 15) can transmit emergency information to a satellite and Motorola has developed a standalone satellite communicator chip that they plan to include in their upcoming Defy 2 phone and make available to other phone makers.

The "Find My Phone" app on your laptop uses a combination of Wi-Fi and Bluetooth signals for indoor positioning, which can penetrate obstacles like walls and roofs effectively. Outdoor GPS devices rely on satellites and can struggle in heavily wooded areas due to the dense tree canopy blocking the GPS signals.

My experience with Earthmate is that it can only show my location when my inReach is on and paired to my phone. If my inReach is off, then Earthmate will not show my location. I can scroll around on maps, but it has no idea where I am.

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Loon Island Outdoors
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I've never had that issue with Earthmate. I've used earthmate on my phone without my inReach device plenty of times. In fact out of all the GPS mapping tools I have on my phone (Gaia, Caltopo, google maps) Earthmate is the only one that consistently pinpoints my location 100% of the time. This year I was driving up to the Obabikca lake put in at Temagami and about 15km from the spot my phone "lost" gps . I fired up Earthmate and it locked on immediately. Gaia and Caltopo?? Nope....