Hi,
Raynac, to give you a little info on the tessen, yes, it was (is) a real weapon. When entering a house, a samurai would remove his long sword, leaving only his short sword in the case of defending himself if need be. However, he would often have one or two other small items on or around his person as well, including (possibly) a jutte, hojo cord, or tessen. In fact, the tessen was probably more common, as the other two were more commonly found on a policeman, and the tessen often doubled as a badge of rank (similar to a jutte, different colour wrappings for the handle could denote position).
The tessen itself was originally just a regular folding fan (known as a sensu), and was a part of regular everyday wear thrust, through the obi. As time went on, samurai began having their fans made with solid iron outside plates, and steel ribs, making a rather heavy impact weapon when closed. Later versions did away with pretence entirely, being a solid iron bar in the shape of a folded fan. It's use has been a feature of a number of classical systems, and it's principles are very applicable to many modern implements you can find around you on a daily basis (say, a rolled-up magazine...).
If you want to get one yourself, I would recommend the one said to be based on one used by Kotaro Yoshida, one he is said to have killed a bear with, and is sold by bugei.com.