I possibly live more remote than you do - but mobile data isn't really a thing (in the UK at least) you can rely on continuously when you're cycling, or visiting the supermarket and you've lost your partner near the cheese aisle...

I mean it is in most of the UK. Maybe not in remote areas of Scotland or Wales.

In most of the supermarkets down here, couple of miles from M25. I mean, outside, so its probably considered third-world country, but no, no need to reduce the argument ad absurdum.

Or 2 metres from the window a mile from Hammersmith. If not for WiFi calling I'd have to leave my phones on the windowsill.

I've still got dead zones near me. If I were cycling with someone, and we wanted to chat on headsets, there's at least a few places I might ride where we'd hit dead air. If we're on different networks, then we both need coverage to communicate with cellular.

Might be more reasonable to use higher bandwidth, lower latency codecs over bluetooth as well?

For this use case, old fashioned radio is a lot more reliable.

Quite likely, but then you need to carry that radio. And probably still carry a phone in case you split up and want to communicate.

You raised reliability issue, you've got a solution, now you're moving a goalpost and raising a convenience argument.

Decide which one is it.

PS Motorola talkabout T62 or T42 - small, light, reliable. Retevis h777: sturdy, reliable. You can just drop them in the bag.

I commonly Signal call my partner when we are at opposite ends of the house. I can see something like this being useful to prevent using some remote Internet server to facilitate a very local call.

I wonder if there's a home lab / self hosted solution for this.

Bluetooth to reach and reliably hold a high throughout connection to the device across the house?

I don't think so.

You can do a surprising amount with a low throughput connection though. I've been playing with Google's Lyra V2 codec - it chews up a fair bit of CPU, but 3.2kbps over a CodedPhy link sounds fine.

On festival sites and other crowded events, cellular sometimes gets quite saturated and slow. This might be a good alternative.

Also, I could see it as a useful tool in emergency situations. But a lot of people would need to use it to be actually useful.

When I last had a university workshop where 20 people in a room worked on a bluetooth protocol I also noticed bluetooth is quickly saturated with many participants. Hopefully that changed in the last 15 years since...

I would love to use it to talk to my girlfriend when we go bike riding. I was shocked by the price tag for all the motorcycle helmet comms systems.

If you're looking at the premium segment then yeah, when you're going out with your several mates and need to be able to hear every one of them.

For one rider to one rider you can get a very decent set well under $100 (Lexin b4fm, FredConn, even Thokwok is well reviewed).

Cardo uses a similar tech for a dynamic mesh network, using Bluetooth I think, in their helmet comms. So if you are out on motorcycles or ATVs you can still talk without needing a cellular network. It makes things a lot more stable and not use any data. In these scenarios you'd struggle to talk face to face wearing helmets without some sort of comm. So if you can remove the need to buy a specialized comm device to do it, sounds great.

You can't. Smartphones are Class 2 devices (weak), and you must use radio the way firmware let's you.

Purpose-built hardware is Class 1 (much stronger, 100 mW/20dBm vs 2.4mW/4dBm), and they can use sophisticated protocols to keep the connection stable. And that's Bluetooth.

If they're not playing Bluetooth but go general ISM, they can emit whole 1W on 2.4GHz or 915 MHz.

They're not really alike.