I reverse-engineered my motorcycle's Bluetooth protocol to put Google Maps on the dashboard

My motorcycle has a Bluetooth instrument cluster. It pairs with the manufacturer's phone app and shows turn-by-turn navigation right on the dash, which sounds great until you actually use it. The nav is routed through a maps provider I don't love, the app is clunky, and there's no way to extend any of it. I kept thinking: it's just my bike talking to my phone over Bluetooth. How locked down can it really be? So one weekend I decided to find out, and a few weeks later I had Google Maps navigation running on the cluster through an app I wrote myself. Here's how that went. There are no docs Of course there aren't. It's a proprietary protocol, and the only reference that exists is the manufacturer's own app, in compiled form. So step one was just watching. I started with a GATT walk on the live bike, which is the Bluetooth equivalent of knocking on every door to see what's there. The cluster exposes one vendor service with two characteristics: one the phone writes to, one the bike sends notifications back on. That's the entire conversation surface. Then I captured the actual bytes going across. Android can log every Bluetooth packet through its HCI snoop log, so I paired the phone with the bike, rode around, and pulled the capture. Now I had real traffic, and absolutely no idea what any of it meant. Reading the app to read the protocol You can stare at hex forever and still guess wrong. The faster path was the app itself. I pulled the APK, ran it through JADX to decompile it, and got something close to readable source. Most of the class names weren't even obfuscated, which was a gift. From there it was cross-referencing: take a message I saw on the wire, find the code that builds it, and work out what each byte is. Frida helped a lot here. It lets you hook a running app and watch functions get called with their real arguments, so I could catch the exact moment the app turned "next turn is a left in 200m" into bytes and shipped them to the bike. Slowly the shape came out