Question: Can the app determine the location of the target device if the option of GPS (Location Service option on that device) was turned off?
Answer: When the target app meet the condition (for example after a interval of 15 minutes), it will try to turn GPS option on to read a record/location of GPS and then will automatically turn off again (restore to old status of GPS option).
However, so far this feature does not work 100%. There are some cases it is not able to turn it on. The developer will invest more time for this feature.