"Device information: information about the computer or mobile device you use to access the Services, including the hardware model, operating system and version, device identifiers set by your device operating system, and mobile network information. With your permission, we may also receive data from your mobile device's health app (like Apple HealthKit or Google Health Connect), including hours of sleep and sleep goals."
Calm collects hardware model, OS details, device identifiers, and mobile network information, and can also access health app data including sleep metrics.