Before initially contacting a business believed to have infringed a patent, the patent owner should have a strategy for following through if the accused infringer does not respond favorably. Otherwise, the patent owner may face severe loss of rights.
A patent owner (patentee) may be precluded from enforcing its patent against an alleged infringer after a period of time from the first notice identifying the patent and possible infringement (e.g., 4 ½ years) if the following conditions are met:
- Misleading Conduct/Silence: The patent owner, through misleading conduct (or silence), leads the alleged infringer to reasonably infer that the patentee does not intend to enforce its patent against the alleged infringer (e.g., by sending a cease-and-desist letter followed by years of silence);
- Reliance: The alleged infringer relies on that conduct; and
- Prejudice: The alleged infringer will be materially prejudiced if the patent owner is allowed to proceed with its claim (e.g., alleged infringer has continued selling and expanding product lines).
This legal doctrine known as patent equitable estoppel applies on a case-by-case basis to each patent asserted by the patent owner. Therefore, a patent owner may have other patents to enforce which may not be barred by equitable estoppel.