Located within the well house are sensors that  monitor the temperature, on/off status of the pump and on/off status of the heater. 
Recording the information from the sensors is a microprocessor that is programmed to look at the sensors and determine there state or read there value.
The physical temperature of the room is read by a device called a DS1620 Integrated circuit.  The microprocessor interrogates the IC via a serial connection every few seconds to get the temperature.  
In the case of the pump and heater it is relay contacts that change states and give the microprocessor a voltage of 0 or 5 volts.

Once the data has been gathered by the microprocessor it is combined and formatted into a data string and sent to a radio transmitter in a serial format.  The radio transmitter is then keyed up and data is transmitted to the house approximately 200 feet away using a beam antenna. 
Note: 
You will notice that the antenna is camouflaged.  The reason for the camouflage is that after I built it and attached it to the building it  stuck out like a sore thumb.   Since I am probably the only person in Iowa with an antenna attached to their well house I decided to keep it as inconspicuous as possible!

Located in my home is an antenna in the attic that receives the data and sends it to a receiver.  This receiver than passes the data to another microprocessor that parses out the information and stores it in variables.  It also has the responsibility of recording my inside home temperature and outside temperature.

Once all the data is collected it is ready to be sent to my website.
Located near the electronics in my home is a computer I have set up as a server. It sole responsibility is to serve my home intranet and connect to the outside world. 
 I have written a program to collect the data from the microprocessor, format it for submission to my web site, connect to the UNIX server of my ISP and upload the new information.

Once the data is on the server it has to be incorporated within my web pages.  To do this automatically, I wrote a Perl script that  places the current information within the page you are looking at.