Can I use GPSLarp with more than one iPhone?
Yes. GPSLarp lists every iPhone it can reach and you choose which one it acts on, from a picker in the app. One phone at a time, chosen by you, for as long as you like.
There is a catch worth knowing before you plug in a second phone, and it is easier to trip over than to recover from: the panel that tells you what is stopping you does not follow your choice. It always describes one phone, and which one is not up to you. If you are still getting a phone set up, attach that phone by itself.
01The picker, and what it shows
GPSLarp asks the connection it holds which iPhones it currently reaches, and puts one entry in the picker for each. Every entry carries three things: the phone's name, whether it is reached over a cable or over Wi-Fi, and the first few characters of its identifier — enough to tell two phones with the same name apart, which is the case the identifier is there for.
Above the list the app says how many it found. With one attached that reads 1 iPhone found, and with more it counts them.
Whichever entry is selected is the phone that setting a location acts on. When the list is refreshed, your selection is kept if that phone is still there, and moves to the first entry if it is not — so a phone being unplugged quietly changes which one is selected, and the picker is the only place that shows it.
The list is phones the connection reaches, not phones plugged in
A phone can be attached to the Mac and absent from this list. The picker is built from the phones GPSLarp's own background connection currently holds a route to, which is a narrower thing than what macOS sees on the cable. An empty list therefore has its own page — GPSLarp can't find my iPhone — and it is about a step earlier than this one.
02The panel that ignores it
Before it will set a location, GPSLarp checks the phone: is it there, is its iOS new enough, does it trust this Mac, is it unlocked, is Developer Mode on, is the support file installed, is the connection running. That check produces the panel you read when something is wrong, and it is what most of this help centre is about.
That check is not given the phone you picked. It asks macOS which devices are attached and inspects the first one on that list. With one iPhone attached this is invariably the right phone and the distinction never arises. With two, the panel can be describing a phone you are not working on.
Two more things behave the same way, and they are the two that act rather than report: installing the support file iOS wants, and asking the phone to reveal the Developer Mode row in Settings. Both are offered from that panel, and both go to the same first phone.
What that looks like when it bites
You attach a phone you have already set up and a second one you have not. You select the new phone in the picker. The panel reports that everything is satisfied — because it is describing the old phone — and the new one is untouched. Or the reverse: you have set the new phone up correctly and the panel keeps reporting a problem that belongs to the other one. Nothing in the app names the phone the panel is talking about, which is what makes this hard to spot rather than merely annoying. It is a known defect on our side, not something you have configured wrongly.
03What to do about it
01While you are setting a phone up, attach it alone
Everything in this help centre about trust, Developer Mode and the support file is about getting one phone ready, and every one of those steps reads the panel described above. Unplug the others and turn Wi-Fi connections to them off. This is the whole workaround and it costs nothing.
02Once a phone is ready, the picker is what matters
Setting a location goes to the phone selected in the picker. If both phones are already set up and you are only choosing between them, you are past the part that goes wrong.
03Check the picker after anything is unplugged
The selection moves to the first entry when the phone it was on disappears. Nothing warns you, so glance at the picker after a cable comes out or a phone drops off Wi-Fi.
04Keep an eye on which phone is where
The picker shows a shortened identifier beside each name for exactly this reason. Two phones called "iPhone" are otherwise indistinguishable in that list, and renaming one in Settings is the cheapest fix there is.
04Other questions this raises
Can two phones have a location set at once? No. GPSLarp acts on the selected phone, and selecting another moves the app's attention rather than adding to it. Stopping is per phone too — see How do I put my real location back?
Does a second phone use another free run? The free grant is one run of each mode, and it is counted against your account rather than per phone. Adding a second iPhone does not add a second set. The whole of that is on What do I get without paying?
Does each phone need its own setup? Yes, and it is the same setup each time: the trust grant is between one phone and one Mac, Developer Mode is a per-phone switch, and the support file is installed per phone and cleared by that phone restarting. Nothing carries over from the first.
Two Macs rather than two phones? Different question. Your saved places live in a file on one Mac and do not follow you — Where are my saved locations kept?
One of them is being held by something else. Only one program at a time may hold the connection to a given iPhone, which is its own page: Another program on my Mac is using my iPhone.
The honest limit of this page: it describes which phone each part of the app acts on, read off the application's own source. It says nothing about what any of those phones does with a location afterwards — nobody in this project has watched that happen on a real iPhone from beginning to end, which is why every account gets a free run of each mode.