Pacif-i, the world's first Bluetooth pacifier, has a range of about 50 feet line of sight. It has a slightly longer range when the coloured front face is facing towards the smartphone than when the teat is facing towards the smartphone. This is due to the fact the antenna is orientated to maximise range forwards, rather than backwards, from the device.
Pacif-i's range will be reduced when there is an obstruction between the pacifier and the smartphone. However it should still be possible to have your baby use the pacifier in one room and be able to read the temperature from it in another.