Ecobee thermostats have the capability of adding a Remote Sensor Module (RSM) that enables you to connect up to 4 remote sensors to your ecobee smart thermostat (EB-STAT-02). The RSM is pre-configured to support the following sensors:
Honeywell C7189U indoor sensor and C7089U outdoor sensor
Tekmar D076 indoor sensor and D079 slab sensor
Johnson Controls HT-6703 humidity sensor
Other temperature sensors can be supported by just entering the B value or the resistance reported by the sensor at 70°F during the configuration process.
Many contractors are using the EB-STAT-02, the RSM, and a remote sensor to monitor the temperature of the loop water in their ground source heat pump. Knowing the water temperature in the heat pump loop can help during troubleshooting on service calls. Also the ecobbe stat can be configured to send out an alert message if the water temperature gets outside of a pre-set temperature range.
One possible sensor a contractor can use for this application that is available from Jackson Systems is an ACI A/AN-BP sensor (picture below). This sensor is 10K ohm at 77°F Type III bullet probe. The probe can be mounted to the water loop and wrapped with insulation tape. The combination of monitoring and charting the loop water temperature and the alert messages from the ecobee thermostat is a win-win situation for the contractor and the homeowner.