What I do not have an apple watch my iPhone are two things: playing a podcast and taking pictures and videos. Upcoming updates of watchOS 5 software solve podcast problems, I have a dedicated camera to shoot without an iPhone. However, it is still a tough situati that you can not combine Apple Watch with Bluetooth car audio.
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My Apple Watch can stream Apple Music and Radio in LTE. You can stream podcasts over LTE. It is paired with Bluetooth headphes and speakers for music and podcast output.
By combining this functi, I can travel regularly without outdoor training or carrying the iPhone. I can not pair Apple Watch with my car stereo, so I'm still hesitating to leave home without my iPhone when I'm driving for more than a few minutes.
Bluetooth car audio is not compatible with Apple Watch from the first versi. Although some car stereos are an excepti, most car stereos are classified as a Bluetooth car system, so they are not displayed the Bluetooth pair setting screen.
iPhone can do it. iPads can do it. Even Apple 's currently disctinued iPod nano (iPod nano that looks like a mini iPod touch rather than something like Apple Watch prototype) is advertised as a feature of Bluetooth pairing including cars. The same thing is not yet the case with Apple Watch.
I do not expect to have Apple Watch project CarPlay or something my car's built-in screen. I still need an iPhone for it. But I think that it is reasable to expect that Apple Watch will be able to send audio to car stereos.
Recent battery life is really good. Watch can play all kinds of audio locally via LTE, clock is already working with Bluetooth speaker.