The privacy of mobile apps has been extensively studied, but much less attention has been paid to the privacy of the mobile OS itself. A mobile OS may communicate with servers to check for updates, send telemetry and so on. We undertake an in-depth analysis of the data sent by six variants of the Android OS, namely those developed by Samsung, Xiaomi, Huawei, Realme, LineageOS and /e/OS. We find that even when minimally configured and the handset is idle these vendor customized Android variants transmit substantial amounts of information to the OS developer and also to third-parties (Google, Microsoft, LinkedIn, Facebook etc) that have preinstalled system apps.