Different patents must be treated individually for purposes of equitable estoppel, regardless of whether claims in a second patent are supported by the subject matter in a first patent when the second patent contains claims of a different scope.
Background / Facts: The patents here are directed to improvements in electronic animal collars. The patentee sent a demand letter to the original manufacturer of a competing collar stating that it infringed a first patent (but did not mention a second relevant patent). The manufacturer responded by contending that one of its other products was “prior art [that] invalidates the claims of the [asserted first] patent.” The patentee took no subsequent action for over four years. In the meantime, the manufacturer continued making and selling its collars, developed other designs, and was acquired by another company. After the acquisition, the patentee issued another cease-and-desist letter to the acquiring company, this time asserting both the first and second patents, to which the acquiring company responded by filing this declaratory judgment action.
Issue(s): Whether equitable estoppel bars the patentee from bringing an infringement claim under either patent.
Holding(s): Yes under the first, but no under the second. Regarding the first patent, the patentee unquestionably misled the original manufacturer through its demand letter and subsequent silence for over four and a half years. Further, precedent clearly establishes that equitable estoppel applies to successors-in-interest where privity has been established, as in this case for the acquiring company. With regard to the second patent, however, the first notice of infringement was not until the second cease-and-desist letter, and there can therefore be no misleading conduct or silence to indicate that the patentee did not intend to enforce the second patent.