Typically, these devices are designed to only send data when the temperature has changed enough. This conserves precious battery life. If you force poll these, you will have terrible battery life. I just checked one of my Iris Motion sensors and it seems to report temperature values once the value has changed by about 1 deg F.
If you want a sensor that doesn't rely on batteries, and allows you to customize the deadband and reporting frequency, you could try one of the following devices. I have two of them and they work very well.
