You may or may not have seen these, they're all over the place including the Audi "styling" section too.
In short they seem to be a small resistor that you bung (note my technical knowledge here) into the air intake sensor socket. This fools the ECU in thinking that it's always cold air coming into the engine and therefore adjusts the fuel mixture to the engine and can produce upto 20hp. Seems a fair theory.
This is my Q to those of you who've had remaps, although the adds refer to it only working on non turbo engines.
Having just had my car remapped last sat, is it likely to have included this type of mod to the ECU already? I know it has something to do with changing the fuel mix values. I have a feeling that i've something similar has been applied with my remap.