An academic research, conducted by Professor Douglas J. Leith from Trinity College at the University of Dublin, analyzed traffic originating from iOS and Android devices heading to Apple and Google servers at various stages of a phone’s operation, such as data shared, founding that Google collects around 20 times more telemetry data from Android devices than Apple from iOS.

According to Leith explanation, the research[1] analized all data that could be collected by both operating system itself and default apps provided by vendors,such as search (Siri, OkGoogle), cloud storage (iCloud, Google Drive), maps/location services (Apple Maps, Google Maps), photo storage/analytics (ApplePhoto, Google Photos), discovering that

both iOS and Google Android transmit telemetry, despite the user explicitly opting out of this option, and this data is sent even when a user is not logged in

The research found also that Google collects a notably larger volume of handset data: during the first 10 minutes of startup a Pixel handset sends around 1MB of data to Google, around 20 time more than an iPhone that sends around 42KB of data to Apple.

This data collection process takes place every 264 seconds on idle Apple devices and once 255 seconds on Android smartphones: almost every four and a half minutes even when the handset is not being used.