> "I assume tracking mobile phones from space would be way harder and more expensive"
I dunno which way I'd bet on that; on one hand any cellphone signal sent upwards is wasted energy, wasted battery - the cell towers are sideways. And cell towers are local so phones will try to use as little power as possible to get to the closest mast also to save battery, 5G picocells can be down to 100 meters. But you can't be sure to radiate sideways when phones are used at all sorts of angles, can you?
On the other hand, signal going upwards has clear line of sight and rapidly thinning atmosphere. A Google result tells me that cellphone base towers can "typically reach up to 25 miles and sometimes up to 45 miles", and this article[1] says cellular macrocells can be up to 100 miles (diameter?). Wikipedia[2] says "Mobile phones are limited to an effective isotropic radiated power (EIRP) output of 3 watts" and Reddit[3] says you can reach the International Space Station as an amateur with 5-10 Watts and a good aerial.
So ... maybe? a tuned sensitive receiver constantly listening for moments of phones doing a high power ping?
Cell phones don't have directional antennas. It is impressive that they fit the anisotropic antennas. You can hold the phone in any orientation and move it around.
The directionality of phone network comes from the towers which have arrays of antennas pointing in different directions.
Also, the cell phone doesn't know where the towers are. Especially with all the smaller cells that may not know where they are.
I dunno which way I'd bet on that; on one hand any cellphone signal sent upwards is wasted energy, wasted battery - the cell towers are sideways. And cell towers are local so phones will try to use as little power as possible to get to the closest mast also to save battery, 5G picocells can be down to 100 meters. But you can't be sure to radiate sideways when phones are used at all sorts of angles, can you?
On the other hand, signal going upwards has clear line of sight and rapidly thinning atmosphere. A Google result tells me that cellphone base towers can "typically reach up to 25 miles and sometimes up to 45 miles", and this article[1] says cellular macrocells can be up to 100 miles (diameter?). Wikipedia[2] says "Mobile phones are limited to an effective isotropic radiated power (EIRP) output of 3 watts" and Reddit[3] says you can reach the International Space Station as an amateur with 5-10 Watts and a good aerial.
So ... maybe? a tuned sensitive receiver constantly listening for moments of phones doing a high power ping?
[1] https://www.emnify.com/blog/5g-small-cell
[2] https://en.wikipedia.org/wiki/Wireless_device_radiation_and_...
[3] https://old.reddit.com/r/HamRadio/comments/rvzj11/can_i_make...