How to find a lost phone in a no-cell-coverage camping site?

Post by juanuicich » Thu, Oct 26, 2023, 1:44 AM UTC

lxgr wrote: post #38

eternityforest wrote: post #26

I wonder how cheap and low power we could make tracking beacons if we didn't actually have to send any data and could accept some privacy risk. Imagine like, an airtag, but the ID only needs to be 1 byte long, or even just a simple presence signal. You'd put it on everything you own that's portable and easy to lose. When you want to find it you just search for signals. Maybe it could have an NFC silencing feature. Pe…

> Imagine like, an airtag, but the ID only needs to be 1 byte long, Well, then you could only ever track 255 different tags :) AirTags are already pretty minimal. Their battery lasts about a year, and I imagine an open source equivalent should be possible to build for under $5. This is purely guesstimated based on the fact that I have a couple of Bluetooth LE thermometer/hygrometers that cost me about $3 a piece that…

Post by jukea » Thu, Oct 26, 2023, 1:45 AM UTC

WanderPanda wrote: post #37

jukea wrote: post #31

I once found my phone buried in the sand on a beach with no coverage. I had a year worth of pictures on it, so I stewed in anguish for almost a day until we thought about installing a Bluetooth signal monitor on a friend’s phone . Given the sluggish update frequency, we resorted to triangulating the phone’s position. As we were pulling it from its sandy grave, I swear it felt like we were cheating fate itself.

Not to nitpick but I think you mean trilaterate ;)

Post by r00fus » Thu, Oct 26, 2023, 1:48 AM UTC

juanuicich wrote: post #71

lxgr wrote: post #38

Earlier quoted context omitted.

> Imagine like, an airtag, but the ID only needs to be 1 byte long, Well, then you could only ever track 255 different tags :) AirTags are already pretty minimal. Their battery lasts about a year, and I imagine an open source equivalent should be possible to build for under $5. This is purely guesstimated based on the fact that I have a couple of Bluetooth LE thermometer/hygrometers that cost me about $3 a piece that…

Apparently there are Find My compatible generic tags coming out of China already, and they cost less than $5, shipping included. I say apparently because I’m still waiting for one to arrive and test.

Post by fsckboy » Thu, Oct 26, 2023, 1:57 AM UTC

jffry wrote: post #51

lxgr wrote: post #40

Earlier quoted context omitted.

If we're being nitpicky it was probably neither – multilateration requires taking multiple measurements, drawing circles/lines of equal signal strength (or timing advance) and then intersecting these. If you just want to home in on a transmitter, there's a much simpler algorithm: Try walking into various directions and keep heading into the one that makes the signal strength nunber go up :) Not sure if there's a name…

> Not sure if there's a name for that. Hill climbing! https://en.wikipedia.org/wiki/Hill_climbing Basically: Go in any direction that makes the number go up. Repeat.

Post by jojobas » Thu, Oct 26, 2023, 2:19 AM UTC

JCharante wrote: post #41

smortaz wrote: post #10

not directly relevant, but was riding my motorcycle in the boonies, and lost the phone which was on the handlebar (bumpy rocky path). Looked for it several times on the path with no luck. Then I remembered my old iPhone was in the backpack. Did a Find my phone on the backup phone and it showed exactly where it had lost touch with the primary phone. This is all without cell or Wi-Fi service. Saved me a $1000.

You might not want to mount your phone on the handlebar. See: https://news.ycombinator.com/item?id=37230198