Today man has developed extensions for practically everything he used to do with his body. The evolution of weapons begins with the teeth and the fist and ends with the atom bomb. Clothes and houses are extensions of man's biological temperature-control mechanisms. Furniture takes the place of squatting and sitting on the ground. Power tools, glasses, TV, telephones, and books which carry the voice across both time and space are examples of material extensions. Money is a way of extending and storing labor. Our transportation networks now do what we used to do with our feet and backs. In fact, all man-made material things can be treated as extensions of what man once did with his body or some specialized part of his body (qtd. in McLuhan, 1995, p.374-375).
It is easiest to see media as extensions of man through an example that Derrick DeKerckhove gave. "When I telephone from Toronto to Munich, I instantly become a 7,000km-wide blind man. When I use video conferencing, I am more completely 'there'" (DeKerckhove, 1995, p.184). This is a perfect example of how media can extend the human body. In the example, Dekerckhove's ear extended via the telephone from being in Toronto to being in Munich. This would have been impossible in the past before the telephone.
Fire fighters use two-way radios in order to communicate at the scene of a fire. In essence when the fire chief gives a command over the radio the chief is extending his or her voice from being outside the building, to being inside the building. When they get a response back from the team inside the building, the radio is extending the chief's ear so that it can reach inside the building to hear the team.
The concepts of the medium is the message and the extensions of man are very closely related in that each time a new extension is created, a new medium is produced which says a lot about society. Before the telephone business on a global scale would have been impossible. By extending the human ear through the use of the telephone, Alexander Graham Bell in effect wrote a message about the world that said that humans would be able to live in geographically sparse areas and still receive information at fast speeds over a wire.