The tracking function of Collector for ArcGIS is here:
The tracking function of Collector does not report when the application is in the background mode.
It stands to reason to preserve the battery on mobile devices.
However, when mobile device is used in car, no cause for worry about battery.
I think that we can select whether Collector reports even background mode is the best way.
Then collector can report log even if I open other application.
Moderators note: This idea has been marked as a duplicate of Option to have Location Tracking on when App is in background by Scott Prindle. Please consider voting on this idea.