In Nautilus v. Biosig Instruments, Biosig had been awarded U.S. Patent No. 5,337,753 for a heart rate monitor for use on exercise equipment. The patent disclosed an improved monitor that could isolate heart signals, which distinguished it from conventional monitors, which could not isolate the electric signals emitted by the heart. Biosig’s invention required exercisers to place their hand in contact with two electrodes on cylindrical bars “in spaced relationship with each other.” Biosig asserted that this claim was definite since a skilled artisan would figure out the correct spacing for isolating heart signals by trial and error.
The Supreme Court, however, determined that this claim was not precise enough, stating that “a patent must … afford clear notice of what is claimed, thereby apprising the public of what is still open to them.” In other words, claims must inform those skilled in the art about the scope of the invention with reasonable certainty. The detail about the spacing of the bars was not specific enough for competitors to know whether they would infringe Biosig’s patent.
This decision could signal a significant change in requirements for patent claims. In the past, courts invalidated claims only when no single construction could be found for a term. Courts accepted a little ambiguity. This gave litigation plaintiffs flexibility to accuse targets of infringing their ambiguous claims.
Moving forward, the new formulation finds patents invalid if the public cannot determine the boundaries of the patented invention with reasonable certainty. The Court expressed that its’ goal was to eliminate a patent drafter’s temptation to be purposely vague and ambiguous.