Facebook has responded to follow-up questions by US Senators in a 222-page long document. The answers reveal some of the intrusive ways in which the social media giant tracks its users in the name of security and better services.

Although almost the whole document focuses on privacy and security concerns raised by the US lawmakers, most startling revelations come in response to Senator Roy Blunt's questions on cross-device tracking.

The social media platform revealed, “We collect information from and about the computers, phones, connected TVs and other web-connected devices our users use that integrate with our products, and we combine this information across a user’s different devices.”

Following are some of the ways in which Facebook tracks its users:

Mouse movements: Facebook records your mouse movement to distinguish you from a robot. The company also uses information such as whether a window is foregrounded or backgrounded to ensure if you are a bot.

Device attributes: The California-based giant obtains information device information including battery level, signal strength, available storage space, file names and types and plug-ins.

Device Signals: The company also tracks bluetooth signals and information about nearby Wi-Fi access points, beacons and cell towers.

Network: Facebook registers the name of a user’s mobile operator or ISP, language, time zone, mobile phone number, IP address as well as connection speed.

Nearby devices: The $550-billion giant said it also obtains “in some cases, information about other devices that are nearby or on their network, so we can do things like help them stream a video from their phone to their TV".

Data from device settings: Facebook tracks user’s GPS location, camera or photos if the permission for these have been given by a user.

The revelations by Facebook follows CEO Mark Zuckerberg’s testimony in US Congress in April in the wake of the Cambridge Analytica scandal.