For anyone reading this and not knowing this; since your post doesn't make it explicit enough, it uses a different APN because Google specifically made it do so. They could let it be hidden. Of course carrier would then mod it in anyway, but here Google did it for them.

I'm fairly sure tethering can also be trivially detected by inspecting the TTL of packets, as a device sitting "behind" the tethering device will increase the TTL by one.

https://android.stackexchange.com/questions/47819/how-can-ph... seems to have more on the matter.

Clever! I hadn't considered that at all. I suspect you mean decrement by one, though.

On Linux:

`sysctl net.ipv4.ip_default_ttl` (mine was 64) `sysctl net.ipv4.ip_default_ttl=65`

Done ;)

This can be spoofed/hidden extremely easily if both devices are open source and you want to change it though. It's not like TTL can't be changed.

The tethering device can just rewrite the packets to hide the tethered device.

Even better - you only need root on either device. Just set a higher initial TTL on your tethered device, or rewrite the TTL on the phone.

But carriers don't use that anymore, too easy to bypass.