People who download iOS 13, the latest iPhone software update, are getting notifications that apps like Facebook are harvesting their data using Bluetooth and other background app activity.

iOS 13, set to launch this week, promises a slew of new privacy measures to notify people when apps are covertly tracking them and to give users more control over what data they share.

Facebook got out ahead of the update with a blog post disclosing details about how its mobile app tracks users.

People who downloaded an early version of Apple's next major iPhone software update, iOS 13, have started seeing an unexpected notification on their device: "Facebook would like to use Bluetooth."

The software update, scheduled to launch this week, is loaded with new privacy features that aim to give people more control over what data they share with apps. Tech giants like Facebook and Google harvest data to better target advertisements, a business model that Apple CEO Tim Cook has decried as the "data industrial complex."

For people who downloaded the beta version of iOS 13 early, the update has already caught apps like Facebook and YouTube employing data-gathering methods that have presumably been in place for a while.

One of these methods is to quietly tap into a phone's Bluetooth technology to track a person's physical location and their proximity to others' smartphones.

Facebook tracks and amasses personal data on users' connections with one another and can combine proximity information gleaned from Bluetooth with GPS data to make inferences about their relationships, TechCrunch reported. For instance, Facebook could log that you spent a few hours near someone else at a private residence and differentiate that relationship from other Facebook users you come into contact with only at an office building.

Beyond hoarding profile data to use for tailoring ads, Facebook could theoretically use the relationship-mapping data in its newly launched dating service, designed to compete with apps like Tinder and Bumble.

iPhone users have the option to turn off location services — including through GPS, Bluetooth, and cell towers — for specific apps, and iOS 13 should provide a more detailed breakdown of which apps access which location services. To use Facebook Dating, however, users must agree to turn on location services.

Last week, ahead of the iOS update, Facebook published a blog post explaining its location-gathering practices and noting that users can turn off location services to prevent the app from using Bluetooth and GPS to track them.

However, even with location services switched off, Facebook could still track a user's location "using things like check-ins, events and information about your internet connection," the post said.

Facebook did not immediately respond to Business Insider's request for any additional comment.