How does it work with a zoned system?

How would it work with a zoned system.
e.g. If you have 3 individual thermostats in a zoned system, would you need 3 ecobee3 or is there another way to set it up

ecobee3 Smart Wi-Fi Thermostat

ecobee3 Smart Wi-Fi Thermostat

Product No Longer Available

No Answers have been submitted