Any question answered...

A dog walking down a street will know what other dogs have been around recently, where they came from and went to

https://youtu.be/mOYZaiDZ7BM?feature=shared

That’s my thinking as well, but I too know nothing.

No. GPS uses a fix on three geo-stationary satellites to calculate your position. Most phones support Assisted GPS which gives a quick fix based on cell tower triangulation, but that’s done simply to speed up the users ability to use their location.

The power management software of the vast majority of mobile phones will shut the device down before the battery is completely emptied, so there will always be some power available. However, I’d be very surprised if the device allowed the GPS chip to stay powered up and recording data if it’s shut everything else down.

yeah, but that's because they stink

#teamkitty

They need a minimum of 4, because you also need to establish the time. A-GPS is partly about giving a sensible starting location (helpful for the numerical solution of the location problem) but also about caching the almanac (ie satellite locations) in a way that is faster to access. The alternative is receiving it from the satellites directly, but this is slow (many minutes).

(Not that this is really related to your actual point.)

Isn't it the cell triangulation that does this rather than GPS

That's what I thought. Isn't GPS too slow and power hungry for this sort of thing?

Some iPhones keep their Bluetooth LE powered up while in battery-dead mode, which allows other iPhones with working GPS and internet to report their presence and location back to its owner, though in theory that's all encrypted and unhackable. It's possible a hacked/compromised iPhone (by super secret government agencies, not the welsh police) could power up its GPS/cellular hardware in dead-battery mode, but any software doing that would still be fighting against the limited energy available from a dead / very low battery.

I'm unconvinced about Strava being able to record anything in battery-dead mode, given its regular unreliablity recording with a full battery.

geo-stationary satellites

GPS satellites are in constantly changing low earth orbits, not least because the only practical geo-stationary orbits are over the equator, which would make traingulation a challenge. The satellites are constantly triangulating their own position (from geostationary ground stations) which adds an extra layer of potential error.

That could be how mine phone worked then? Liz and I share an account and are each others ‘hot spot’ thingy. And we were walking together, so could that be it? All I know is I try to remember to charge my phone more often now.

No, the data from that feature won't be available to Strava. But if you both recorded and uploaded to Strava, it will show a combined track for your group. If you look more closely I'd expect you to find your personal track ends when the battery died and the rest is just her.

Freelancey tax question:
I'm a freelance designer. I also do the odd bit of Djing here and there. The places I DJ at require me to invoice them, which im doing through my usual invoice system, for convenience. It's not that much per month and I can't see it making much of a difference to my tax bill, but I did wonder if I could be cheeky and count records as a work expense. Should I ideally be separating these two lines of work if I wanted to do that (not worth it) or can I get away with it?

Wikipedia disagrees?
https://en.m.wikipedia.org/wiki/Cellphone_surveillance

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Not there it doesn't. That just means that any (powered up) phone that connects to a cell tower will share some very basic info about the phone and SIM to be able to use the tower, they have to know who they're talking to. If police know the identifiers of the phone they can see what towers it was connected to and when and get a location, more towers nearby the more accurate it'll be.
I've always assumed that's how rough locations work for no GPS stuff like weather apps, with an occasional GPS check for stuff like Google timelines.

Depends on the meaning of 'not actively in use'. Sounds a bit woolly.

I think not actively in use means not talking or downloading specific data, rather than switched off, phones are constantly doing background stuff when in your pocket on standby.

I'm not sure what the point is here? Mobile phones connect over the cellular network to do voice and data, which is what the Wikipedia article is describing (as basically a network cell will record all devices that are connected to it at a given time and log that). But that data only indicates that a phone was in the area covered by that particular base station, it can't accurately say whereabouts in the cell the phone is. You can get an approximate location, accurate down to about 10 metres, by triangulating the data from the adjacent cells, but it's not as accurate as GPS, which is accurate down to 1 metre.

did wonder if I could be cheeky and count records as a work expense. Should I ideally be separating these two lines of work if I wanted to do that

Probably one for the tax returns thread

can I get away with it?

You can get away with almost anything if your total activity is small enough to be the subject of a two line tax return and your revenue:expense ratio is within a couple of standard deviations of the median for the kind of activity you say you're doing.

From recollection, I know years ago the DJs I worked with claimed records as an expense. From the business perspective they are consumables as they go out of date / fashion, I think was the argument. I think their returns were solely for the DJ work though

But that data only indicates that a phone was in the area covered by that particular base station

Signal strength is usually recorded too, along with round-trip-times. With a whole series of that data it's possible to get a rough idea of a phone's path through a cell area, especially when combined with data from neighbouring towers.

This is after-the-fact analysis though and works well for analysing simple transits through the area covered by a cell tower. It's not great for instantaneous location (stuff like [advanced] forward link trilateration is way better), or when the phone is dawdling within a single cell tower's vicinity for a long period.

Anyway. Enough tin-hattery. Mobile phones are rarely completely spent when it seems they won't charge. The power buttons are software controlled, not hardware, so there's usually enough power to keep the circuits that handle power button polling going. But this is a miniscule amount of power compared to receiving and processing GPS signals, listening for nearby bluetooth devices, let alone powering the baseband modem to send data out over 3G/4G/5G or Wifi.

In movies you are meant to snap your phone in half and throw it in a river, but I think the key element is really the sim card

GSM IMSI (SIM) and IMEI (phone) IDs are both available to the network and so also law enforcement. IMEIs with lots of associated IMSIs probably get flagged as interesting.

Car hire in Corfu? There seems to be an overwhelming choice at the airport... all much a muchness?

Ah yes, I forgot there was a thread for this!

I have a feeling it’s small enough to be fine. I don’t have huge expenses so my ratios are fine in that respect.

@andyfallsoff I think the main thing that makes me unsure is that DJing is only a tiny part of my income, and I’d pretty much be spending as much on records as I’d be making from them.

I'm not an expert but I don't see that it matters what the work is if it's all freelance. You have income and you have expenses. Smush it all together, I assume overall your expenses are lower than your income?

Yes, I guess it's not like my returns are itemised. My overall expenses are pretty low on average I'd say.