Overturning a district court’s finding of prosecution history estoppel, the U.S. Court of Appeals for the Federal Circuit held that an allegedly disclaiming statement made during prosecution was not a “clear and unmistakable” disclaimer to one skilled in the art. Elbex Video, Ltd. v. Sensormatic Electronics Corp., Case No. 07-1097 (Fed. Cir., Nov. 28, 2007) (Moore, J.; Cote, J., dissenting).

The district court ruled that an allegedly disclaiming statement made in response to an office action limited the claimed “receiving means” to a “monitor” that receives the first code signal. The lower court concluded that “whether by mistake or otherwise,” the inventor “agreed” to limit the “receiving means” to a “monitor” that receives the first code signal from a camera. Although the district court acknowledged that obvious errors in statements made before the U.S. Patent and Trademark Office (USPTO) are not necessarily binding, it concluded that the patentee’s statements were nevertheless binding since the prosecution statements “would not have been viewed by one of ordinary skill in the art to be obvious errors.”

The Federal Circuit reversed, finding that the “receiving means” was not limited to the “monitor” because the allegedly disclaiming statement did not amount to a “clear and unmistakable” surrender of claim scope for three reasons. First, the Court noted that the allegedly disclaiming statement was unsupported by “even a shred of evidence from the specification.” According to the Court, there is “nothing in the specification to suggest that the first code signal ever reaches the monitor.” Second, the Court conceded that, when read in isolation, the statement in the prosecution history could be argued to be a disclaimer. However, the Court concluded that, when the prosecution history as a whole is considered, the inventor’s response to the USPTO is not clear. The Court noted that two paragraphs after the alleged disclaimer, the inventor made another statement that implies that the “receiving means” is not limited to a “monitor” and this other statement “is fully supported by the written description and provides further indication that the earlier statement in the same document was not a clear and unmistakable surrender.” Third, the Court observed that, if the “receiving means” was limited to a “monitor,” then the disclosed device would be inoperable because the second code signal from the monitor would never reach the cameras. The Court noted that “[e]ven [the alleged infringer’s] own technical witness testified that he ‘ha[d] trouble figuring out how [transmitting the code signals to and from the monitor] would work.’”

Judge Cote dissented. In his view, when the prosecution history and the patent are considered together, the evidence is “clear and unambiguous” that the allegedly disclaiming statement made in the response was a “strategic choice and an unmistakable surrender of claim scope” and thus the patentee should not be allowed to recapture what it chose to surrender during prosecution in order to obtain a patent.

Practice Note: For prosecution history estoppel to apply, the alleged disavowal must be “clear and unmistakable” to one skilled in the art. Statements made during prosecution that are ambiguous and inconsistent with the rest of the intrinsic evidence may not amount to a “clear and unmistakable” disavowal.