IAT sensor "chip"???

What is an IAT sensor?? All these performance ''chips'' are just resistors hooked up to the IAT sensor. What does the IAT sensor do?? And what do those resistors do when they're hooked up??
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=42604&item=7934180257&rd=1
Thanks!

They dont do much of anything.....save your money!

IAT = INTAKE AIR TEMP

The idea of using a resistor is to fool the sensor into thinking that the air entering the the motor is cooler then it actually is.

right. Voltage = Amps X Resistance. Amps are always constant, so the more or less resistance you have, the more or less voltage you have, and that's how the ECM knows what temp. it is - by how much voltage is coming across. You can fool the ecm with different resistors, making the ECM think the engine needs more fuel when it doesn't, giving you more power. But I agree, they're worthless, save your money.