An Implied Consent law means that when you as a driver obtain the privilege to drive, you also "impliedly consent" to being tested for alcohol use while you are driving. If you refuse to be tested - say you are pulled over and an officer requests you "blow" for a roadside breath test, you will have violated that "implied consent" and face a fine, or restriction of your driving privilege, or both, depending on the State.
In Kansas, however, the supreme court has struck down the violations, on the basis that they violate a driver's right to unlawful search and seizure under the Fourth Amendments to the Constitution.
Article here (via reason hit & run blog).
From the article - with my commentary in italics:
In the absence of consent or a special justification, searches (of a person or their property) generally
require a warrant. That is why every state has an "implied consent" law
saying that drivers, in exchange for the "privilege" of operating motor
vehicles on public roads, agree to be tested should they be arrested
for DUI. If they refuse to cooperate with alcohol testing, they can lose
their licenses through an administrative process. Kansas is (or was)
one of 13 states that also treat test refusal as a crime.(Michigan does not treat it as a crime, it's an administrative loss of driving privilege. In Michigan, your license will be suspended by the Secretary of State, and you will face that for one-two years, even if you are never convicted of the underlying charge of DUI/drunk driving.)