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.