A 2 in 1 environment sensor from Bosch with temperature and pressure is one of the best environmental sensors available. It is low cost and super accurate : +-1hPa and 1C. This sensor can also be used to determine altitude with a high degree of accuracy (+-1M) thanks to the accuracy of the pressure sensor.
The BME280 is the latest model in the series(BMP085/BMP180/BMP183) and supports the I2C protocol for easy wiring and interfacing.
Wide ranging voltage supply of 1.71V to 5V makes it an ideal for use with batteries (2032 coin cell or 2xAA) and many microprocessors. Very low power consumption while asleep (0.1uA), and during measurement (714uA pressure, 350uA temperature). 3 power modes offer different power options.
Wiring diagram for Flex RF Module(not included) to BME280 Sensor