There are many ways to send data from sensors to the outside world via an Arduino, and one inexpensive method is with twitter. You can combine almost any sort of data and text message into a message up to 140 characters in length, and broadcast it to be followed by yourself or other interested parties with a twitter client on various devices or a web browser.
To explain this in simple terms, Carl and Steve from the hackshed website have posted some demonstration code that uses a temperature and humidity sensor and sends the resulting data for all to see if required. Doing so is simple and just requires a sensor and an Ethernet-enabled Arduino board.
When putting together your next Internet-enabled Arduino project - save time, space and money with the Freetronics EtherTen. Apart from being fully Arduino Uno-compatible, it has onboard Ethernet, microSD socket, full USB interface (so you don't need a costly FTDI cable just to upload a sketch!) and supports optional Power-over-Ethernet.