Hi Manuel,
As each zone is unique, with different plants, sunlight and soil conditions, we recommend to place one sensor in each zone for best watering results. If you have many zones, consider adding sensors for the zones that you care most. In the current version of the app, we allow one sensor to monitor up to 3 zones but the user needs to make sure the zones have similar environmental conditions.
BTW, we have Black Friday deals going on at this moment. Thanks for the question.
Regards,
Netro