This device though a toy, provides a significant opportunity to familiarize someone with the look and feel of a polygraphs physical attachments. The exception being blood pressure, but for a quick trip to a drug store,  add a blood pressure meter and low and behold all 4 sensors of a polygraph. This strategy combined with polygraph research, and countermeasure practice, makes for a very successful combination. So even if it doesn't work, familiarity with the device and the phases of the polygraph exam, removes many layers of anxiety and fear. Which in all reality is the truest and best countermeasure.

I bought this.

It kept giving me puzzling read outs.  So I ran it without the sensors attached to anything.  It seems like all the questions should have come out the same, undetermined, truthful or lie.  But of the 21 questions, 4 came out as lies, 2 as undetermined and the rest as truthful.

It's random.  It's a toy for laughs at parties.  But if you use it to train yourself, you are going to get anxious because no matter how you control you biological responses, you are going to come up with lies.

I even stabbed myself with a pin and held my breath for 7 seconds--made no difference, got no response.   

Don't waste your money.

What do you think of this machine for practicing?

http://www.ninjagizmos.com/products/Cubicle/USB_Polygraph