Having the app in the foreground means that your screen is not locked and the app is on your screen. Having the app in the background means that you can be using other apps or your screen can be locked.
If you are an Android user
TraceTogether works in both the foreground and background.
If you are an iOS user
TraceTogether works best in the foreground. We recommend users keep TraceTogether open in meetings and crowded places. iOS users can also activate the in-app "Power Saver Mode” (see images) to keep TraceTogether in the foreground with a dimmed screen while communicating with other TraceTogether-enabled devices. If you need to use other apps, just remember to switch back to TraceTogether once you are done.
Why did we create the TraceTogether "Power Saver Mode" for iOS devices?
When TraceTogether is in the background on iOS devices, the frequency of scans decreases to improve battery life and to protect user privacy.
Power saver mode