Lexmark v. Static Control
The 2004 case in which a printer maker tried to use the DMCA to stop refilled toner cartridges, and lost.
Lexmark printers demanded a chip in the cartridge that answered an authentication handshake and carried a tiny Toner Loading Program. Static Control Components sold a replacement chip, Smartek, that copied both the handshake and the program so refilled cartridges would work again. Lexmark invoked the DMCA's ban on circumventing technical protection measures and won a preliminary injunction in 2003.
The Sixth Circuit vacated it in 2004. The program was a few dozen bytes dictated by function and barely copyrightable, and the printer's own firmware could be read out freely — so the chip wasn't controlling access to any work at all. The DMCA was a copyright statute, not a tool for locking down consumables. The feud carried on elsewhere and reached the Supreme Court in 2014, by then as a false-advertising case.