Andre Derouchie says:

Hey guys,
No a remote car starter WILL NOT void your factory warranty!! This is a myth... and a lot of dealerships will tell you this. The truth is, they don't want the average joe or backyard mechanic attempting to install one. New vehicle electronics are becoming very complicated and require a lot of specialized equipment. We do work for many dealerships in town. We have licensed installers and back all of our work with a lifetime warranty. There was actually a law passed that prevents dealerships from voiding your warranty for aftermarket add-ons. I have heard all kinds of stories from customers; such as, if you change your own oil, it will void your warranty... doesn't happen. The only way that a system can void your warranty, is if it actually causes damage to a factory part (which, in such a case, we would pay the bill of course). It has never happened, but mistakes can occur. We are human too.

Will installing a remote car starter system void my vehicle new car warranty?

NO. ABSOLUTELY NOT. Voiding your vehicle's new car warranty based on the addition of any aftermarket accessory would be a violation of the Consumer protection laws. Dealers will often make this threat in order for the consumer to purchase the add-on from them. To void your warranty, the dealer would have to prove in court that the remote starter had a direct impact on whatever part or parts that you wanted changed under warranty. And a properly installed remote car starter system cannot have any negative effects on your vehicle.

Magnuson Moss Act

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 manufacturerís product may be used. To challenge a false claim, ask the person to put it in writing, or request the vehicle manufacturerís 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 consumerís 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
  1. the warrantor satisfies the Commission that the warranted product will function properly only if the article or service so identified is used in connection with the warranted product, and
  2. the Commission finds that such a waiver is in the public interest.
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.