I’ve recently been playing with the Electric Imp platform of Internet of Things devices. They’re fairly inexpensive, and very easy to use, so when SparkFun recently was having a sale, I picked up their Weather Shield, and Sensors.
With some slight modifications for power savings, and hooking up the Arduino shield pins to the appropriate pins on the Electric Imp, then it came down to coding it up so the Imp would sleep for five minutes, wake up, take a reading, connects to the wifi and send the data to my logging server, then sleep again.
I packaged the whole thing up in a mason jar for weatherproofing.
The power source is a lithium primary battery, which should last a number of years with the low power consumption the Imp uses while sleeping.
My logging server collects all the data, and generates graphs for easy consumption.