Just be aware that if using two of the same model (ex: WS-1200) the Observer may sync with the different indoor sensors if they are close together.
I have two different models, WS-1001 and WS-0900 and each has its own ObserverIP. There was an issue that one ObserverIP keep grabbing the indoor sensor of the other unit. The way around was to one sync one array and sensors to an ObserverIP at a time. Then put the batteries in the second unit and sensors and sync with the second OberserverIP.
The dashboard goes by the MAC address of each unit.