Plenty of Bluetooth adapters are designed for a specific headphone model and sit flush against the cup without additional wires. When they're attached, it's eas

Plenty of Bluetooth adapters are designed for a specific headphone model and sit flush against the cup without additional wires. When they're attached, it's easy to forget that they're not built in. See https://thebtunes.com/ https://thebtunes.com/ for example. A huge caveat is that if the headphones have ANC, you now have two sets of batteries and two power switches to worry about, so they're a lot less seamless.