If it only supports one sensor, then it wont have a sensor ID, but will have a rolling code .
This is to prevent someone else who lives nearby and has the same weather station from interfering with your weather station.
When you put the batteries in the sensor , the sensor generates a random number and includes that number in its transmissions.
When you tell the weather station to search for a sensor it simply searches for the first transmission it finds, and then remembers the random number,
and then only responds to subsequent messages with that random number in them.
The logic is that as the sensors transmit infrequently, the odds are that if you put the batteries in the sensor and then ask the indoor unit to search for it
it will find yours first rather than another one .
The random number changes every time the sensor is powerd up.