Under the Magnuson-Moss Warranty Improvement Act, a vehicle manufacturer may not make its vehicle warranty conditional on the use of any brand of security system unless the manufacturer provides the system free of charge or the Federal Trade Commission (FTC) has specifically published that only the vehicle manufacturer's product may be used. To challenge a false claim, ask the person to put it in writing, or request the vehicle manufacturer's security system free of charge. If you are charged for the security system, or they refuse to give you a written statement, there may be a violation of Federal law.
This is the actual language of the act:
No warrantor of a consumer product may condition his written or implied warranty of such product on the consumer's using, in connection with such product, any article or service (other than article or service provided without charge under the terms of the warranty) which is identified by brand, trade, or corporate name; except that the prohibition of this sub-section may be waived by the Commission if:
The district courts of the United States shall have jurisdiction of any action brought by the Attorney General (in his capacity as such), or by the Commission by any of its attorneys designated by it for such purpose, to restrain (A) any warrantor from making a deceptive warranty with respect to a consumer product, or (B) any person from failing to comply with any requirement imposed on such person or pursuant to this chapter or from violating any prohibition contained in this chapter.