How does a lie-detector work?

I had my bro ask me a very interesting question today, when watching a movie, "How does a lie-detector work?". And, I didn't accurately know how it worked. So, here I was on my favorite place on the internet, Google ;-) Not surprisingly here to ask question in perspective. Here is a very terse explanation on how it works: http://science.howstuffworks.com/question123.htm

A lie-detector or a poly-graph has multiple sensors recording various readings of the person and these readings are sketched on a plain paper. Change of person's state results in deviation from the standard. The accuracy of the lie-detector's results are subject to the reader.
You can find other interesting results on the same page. Enjoy reading.

Let there be peace. .::V::.
Cheers to Life!
~M~