Measuring temperatures & humidity in all rooms is necessary to monitor and maintain the comfort level. My Home Automation system gets input about those 2 (temperature and humidity) from all kinds of sources.
The main source however are about 10 Oregon Scientific sensors which look like this:
These sensors transmit both a temperature value and humidity value with an interval of ~40 seconds. I use a RFXCOM receiver to receive the information and decode it with a NodeJS script. From there the information is fed to my Home Automation system.
But not only those Oregon Scientific sensor provide information – so does our Honeywell Thermostat, the Mobotix security camera outside, our Central heating etc.
The temperature/humidity information and used for various things.