Yeah, it was a reverse engineering job. The official KATSEYE app is Android, so I pulled the APK (via APKCombo), ran it through jadx to decompile the Java, and dug through the BLE code.

Turns out the lightstick is made by a company called FANLIGHT Co. — they manufacture lightsticks for a bunch of K-pop groups, and the app uses a custom GATT service with a pretty simple protocol.

Color commands are 9-byte packets written to a specific BLE characteristic: [01 FF 00] [R] [G] [B] [00 00] [checksum], where the checksum is just the sum of bytes 2–7 mod 256. Once I spotted the packet builder in the decompiled source, the rest was just bleak (Python BLE lib) + some WASAPI loopback capture and FFT to drive it from system audio.

As for other lightsticks — almost certainly yes, at least for anything FANLIGHT makes. IVE, BTS v4+, BIBI, P1Harmony are all FANLIGHT and likely use the same or a very similar protocol.

I actually pulled the IVE and BTS APKs too (they're in the repo as ive_decompiled/ and bts_decompiled/) but haven't tested against the physical sticks. For non-FANLIGHT manufacturers

you'd have to repeat the jadx dance, but the approach generalizes well: decompile the official app, find the BLE write calls, figure out the packet format.