The BMP085 is a barometric and temperature sensor. I’ve got one on a breakout board from geeetech. Using this and an arduino, it is possible to build an electronic barometer.
It can be connected to an arduino uno or nano:
BMP – Arduino
VCC – 3.3V
GND – GND
SCL – A5
SDA – A4
This will report the temperature and barometric pressure (in Pascal) on the serial port. It is also possible to combine this with a DHT11 (or DHT21 / DHT22) sensor to also get a humidity reading. See https://github.com/sickel/DHT_BMP085. The DHT has to be connected to +5 and gnd, signal to port D2 on the arduino. The DHT library can be downloaded from arduino.cc.
This work has been done in Arduino 1.0.1 on a debian system.