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Comment by donatj | Hacker News Reader

My friend was going through a pretty massive depression after his mom passed. He'd been with my wife and I at our house for a number of hours talking through it, and apparently not texting his sisters back. They called in a welfare check.

We live in a reasonably dense suburb. Police showed up at our front door and asked to speak with him. They just wanted to make sure he was doing OK. He asked them "how did you find me?" and their response was just "we pinged your phone".

Watching my security camera, they did not stop at any of my neighbors houses first. It was very direct to my front door. This leads me to believe whatever sort of coordinates they had were pretty spot on. His car was parked well down the block and not in front of our house so that was no give away.

This was five years ago and always struck me as a "Huh"

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Oh! So IIRC it used to be that the modem could only get a rough estimate of your location and typically Apple/Google's location infra(which combined wifi/blue and lately satellite position based shadow mapping) to determine a precise location. And law enforcement got precise info from _that_ infra(E911 requirements for every device).

Clearly they don't need that now because 5g cell towers have gotten precise enough? Also, if that's true then 5g being that precise might still not apply to urban dense areas, where more postprocessing is required to get better location accuracy...

5G isn’t inherently any more precise, but because of the higher frequency used in 5G, the radio signals are blocked by obstructions much more easily, so there must be many more 5G radios per unit area to provide coverage. And one feature of having many more base stations around is that triangulation of specific phone is much more accurate and precise because of how close the 5G base stations are to all 5G phones.

5G infrastructure isn’t limited to tall easily visible radio towers like 4G and before; 5G transmitters are small and relatively inexpensive, making them very common. My employer has a private 5G infrastructure, and we are not related to telecommunications in any way.

> but because of the higher frequency used in 5G

For the most part they use the same or lower frequencies. N71 (600mhz) is lower than any of the 2G/3G bands and requires less cell density than 3G (UMTS/WCDMA) did.

> 5G infrastructure isn’t limited to tall easily visible radio towers like 4G and before;

Nor were earlier technologies. DAS systems get used in large buildings/cities and were done with 4G as well. Small cells and femtocells have been a thing since at least 3G era.

> 5G transmitters are small and relatively inexpensive, making them very common.

Transmitter cost wasn't the primary limitation before, the options for unlicensed/lightly-licensed spectrum were low before and the standards weren't really designed to use them as primary carrier until NR. Also you had to run way more components to run earlier technologies, the stack is just smaller for a NR deploy.

oh dang i was way off. thank you

This is not true, 5G has multiple positioning improvements that are not related to higher frequencies. 5G has something called LMF (Location Management Function) that handles positioning of user clients through multiple means, like round trip time, angle of arrival, and dedicated 5G positioning reference signals.

You can read more about 5G positioning here:

https://www.ericsson.com/en/blog/2020/12/5g-positioning--wha...

https://www.ericsson.com/en/blog/2024/11/5g-advanced-positio...

https://arxiv.org/abs/2102.03361

https://research.chalmers.se/publication/542739/file/542739_...

i swore 5G used much higher frequencies (and is therefore blocked by so many more things that don't affect 4G and below.) I'm glad I'm wrong, thank you.

In 2009 I worked with a triangulation system in a dense populated area. The precision of location was comparable in average to GPS (meaning sometimes better) when indoors, it was orders of magnitude better as GPS. That was 3G, some yeras ago… I assume today is much better, as the density of cells increased

I'd be very interested in more info, but am going to doubt this for now. Usually just the intra-day deformations of the terrain between the towers through hydrological activity should far exceed what GNSS can achieve.

It is just VERY VERY hard to beat the predictability of orbits.

Does his sister know where you live? General area+basic knowledge = most likely address.

Did the sisters know where you lived? Curious if the police provided them with an area and the sisters were able to give a proper address?

Why is it so hard to believe that the police can use our devices to backtrack us, as both carriers and police officers have said numerous times?

Occams razor

says that police can locate phones

To be honest I thought OP said they lived in an apartment; a house is a different story.

Did he connect to your wifi? That would give the exact property to go to instead of via gps.

But the pinging of the phone would not share ip address

E911 would get bssid of the access point.

If they called. I'm not sure 911 can initiate a call back to a device that hasn't called before.

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