The other day my mom was at our house, parked next to me. She got in her car to leave at the same time I did. I pulled out my phone and put on some music - noting that it was weird that I needed to do anything at all, typically it just resumes playing as soon as it connects to Bluetooth.

But I didn't get any audio. That's weird. Until she drove away and the music started playing through my phone's speaker a few seconds later, and I realized that it connected to the wrong head unit.