The majority of this code actually comes pre-installed in an Arduino add-on library as the 'transmitter' and 'receiver' examples in the 'Virtual Wire' library. The library can be downloaded here. Go here if you do not know how to install a new library. All that we have to do is change when to send a message, since we only want it to send when the reed switch has no magnet near it, or the door is open.

Transmitter

In the transmitter sketch, we added a boolean variable called 'lastReed' that will just keep track of the last state of the switch at the end of the loop, this will allow us to detect a falling edge as the magnet goes away. We also setup pin 6 as an input. The loop section was changed to the attached picture. The actual sketch file is attached as well. All we had to do was add an 'if' statement so we would send the message on a falling edge of the input signal. We also changed the message to something meaningful, in my case, 'door opened'.

Receiver

On the receiver side, all we do is comment out a couple of unneeded 'Serial.print' lines and added one 'Serial.write' line to print out our message. This sketch is also attached.