Open source smartwatch integrates ESP32 MCU with e-paper display

♯ No extra device to remember to charge (unless, perhaps, you have big noise-cancelling cans).

♯ No running out at an inconvenient/irritating time if you don't charge them (or are just out for a long time).

♯ Standard fitting so anything can plug in, makes carrying a spare set (or buying one in an “emergency”) inexpensive.

♯ Easily plug in a double+ adaptor too (not seen it for a while that I remember, but there was a spate of people on public transport listening to the same music that way). Try that with BT.

♯ No pairing issues (tell me you've never had them, even with supposedly good quality kit, and I'll call you a lier!).

♯ Easily switch between devices (my headset doesn't always want to connect when I switch from work to personal phone, so I have to go through the BT-on-and-off-again-at-both-ends dance. At least these days decent devices (and most cheap ones) remember multiple pairings, it used to be even worse.

♯ The crackling from a poor connection was rare with a good jack+socket in my experience, and BT is not immune to interference in busy environments. I've also experienced BT dropping out temporarily if devices get too close (i.e. I sit and bend to adjust a shoelace while my phone is on a trouser pocket).

And of course there is little reason not to have a standard jack as a fallback option, even if you do usually use wireless playback.

With wireless headphones, it's always a question, do I have enough battery for this trip, what to do if I run out of the battery, the answer is usually just taking additional wired earphones with me, just as a backup.

The same reason is why I use wired mouse and wired keyboard, I don't want to have to think about the battery nor knowing that there will come a time when I'll have to change the battery or charge the keyboard.

As others have mentioned, there are benefits to wireless devices, but everything has a Yin and a Yang, you get wireless but you trade something else in exchange.

USB Audio Class has been almost universally supported in computing devices for literally decades at this point, as has USB HID Class which supports media controls.

I have no idea whether Apple allows it to work on iOS devices, but a car head unit could easily expose a USB audio class device and it'd "just work" with Android, Windows, MacOS, etc. devices. Add a USB HID "keyboard" that can send media/telephone inputs and you're good to go without any new tech required to be invented. Works with anything that doesn't go out of the way to prevent it from working. All you'd be missing compared to Bluetooth A2DP/AVRCP would be communicating media info back to the head unit, which is more of an optional nicety rather than a necessity.

Plug a USB cable in to whatever computing device you want to source audio from and it would work great.

Unfortunately the majority of the non-technical community, and a surprisingly large amount of the technical community, acts like they're allergic to wires. I honestly do not understand the demand for wireless charging, wireless AA/CP, etc. when a single cable works better for both. It's not that hard to plug a phone in when you sit down in your car.

I haven't timed it super precisely (my off-state is 30 min and my on-state is 4-5 seconds), but definitely going to check this for thoroughly in my next project, which will wake from deep sleep on button press; curious if there's some delay as everything powers on.