In the October 2004 case of Lexmark v. Static Control Component, the 6th US Circuit Court of Appeals in Cincinnati overturned a lower court ruling that prohibited Static Control Component Inc. from manufacturing microchips for Lexmark ink cartridge replacements. Static Control reserve engineered one of Lexmark's toner cartridges in order to compete and create a cheaper product. The three-judge panel noted, "Lexmark failed to establish likelihood of success under the general copyright statues or under the DMCA." According to Judge Gilbert Merritt, "Congress did not intend to allow the DMCA to be used offensively in this manner, but rather only sought to reach those who circumvented protective measures 'for the purpose' of pirating works protected by the copyright statute."
In a similar case from August 2004, Chamberlain Group Inc. v. Skylink Technologies Inc., a Northern District of Illinois US District Court ruled that Chamberlain Group, a garage door manufacturer, could not prohibit Skylink Technologies from manufacturing a universal garage door opener. Chamberlain Group filed the suit on the claim that Skylink Technologies violated the DMCA by selling a device that circumvented their access controls. For more info, see the Electronic Frontier Foundation website.
Also see this article by Jonathan Band (PDF), Partner, Morrison and Foerster, LLP, on the decisions of these two DMCA–related cases.