Shenzhen Chenghang Electronic Technology Co Ltd v. Notrox LLC

I. Executive Summary and Procedural Information

• Parties & Counsel:
  • Plaintiff: Shenzhen Chenghang Electronic Technology Co., Ltd. d/b/a EVERPLUS LLC and Shenzhen Cuiwei Fenfang Trading Co., Ltd. d/b/a FENFANG SHOP (China)
  • Defendant: NOTROX LLC and FLIPLOK, LLC (Texas)
  • Plaintiff's Counsel: Glacier Law LLP
• Case Identification: 4:26-cv-04647, S.D. Tex., 06/11/2026
• Venue Allegations: Venue is alleged to be proper as Defendants are Texas limited liability companies residing in the district, and a substantial part of the events giving rise to the action occurred in or were directed from the district.
• Core Dispute: Plaintiffs seek a declaratory judgment that their door security product does not infringe and that the asserted patent is invalid, following receipt of an infringement notice from the Defendants.
• Technical Context: The technology involves mechanical reinforcement locks designed to provide additional security for inward-swinging doors against forced entry.
• Key Procedural History: The complaint alleges that on or about June 2, 2026, Defendants, through a brand protection agent, sent an enforcement email accusing Plaintiffs' Amazon product of infringement and demanding the listings be removed. The complaint also asserts that the accused product was first sold in October 2018, more than three years prior to the patent's November 2021 application filing date, which may form the basis of an on-sale bar invalidity defense.

Case Timeline

Date	Event
2018-10-20	Launch date of Plaintiffs' accused product on Amazon
2021-11-05	U.S. Patent No. 11,447,993 Priority Date
2021-11-22	U.S. Patent Application No. 17/532,418 Filing Date
2022-09-20	U.S. Patent No. 11,447,993 Issue Date
2026-06-02	Date Plaintiffs received Defendants' enforcement demand
2026-06-11	Complaint Filing Date

II. Technology and Patent(s)-in-Suit Analysis

U.S. Patent No. 11,447,993 - "Door Security Device"

• Patent Identification: U.S. Patent No. 11,447,993, "Door Security Device," issued September 20, 2022.

The Invention Explained

• Problem Addressed: The patent addresses the need for improved supplemental security for inward-swinging doors, which are vulnerable to forced entry, particularly when an occupant has been induced to unlock primary deadbolts '993 Patent, col. 1:15-44 Existing solutions like security bars are described as "large and cumbersome," which deters their use '993 Patent, col. 2:53-56
• The Patented Solution: The invention is a door security device comprising a mounting plate fixed to the door jamb and a "locking swing plate" that pivots on a hinge pin '993 Patent, col. 2:17-29 In the locked position, this swing plate rotates to abut the interior surface of the door, blocking it from opening '993 Patent, col. 10:55-62 A key feature is that the locking swing plate is "biased by force of gravity" to fall into a "lowermost locked position" where it is retained by features on the mounting plate '993 Patent, abstract '993 Patent, col. 9:45-55
• Technical Importance: The design aims to provide a robust, non-cumbersome security device that automatically settles into a secure, locked position using gravity, simplifying its operation for the user.

Key Claims at a Glance

• The complaint focuses on independent claims 1 and 10 Compl. ¶32
• Independent Claim 1 Essential Elements:
  • A mounting plate with a set of first receiver ears and bays.
  • A locking swing plate configured for pivoting movement between locked and unlocked angular positions.
  • The locking swing plate is also configured for "translation movement along said hinge pin vertical axis between an uppermost vertical position and a lowermost vertical position."
  • The locking swing plate is "positively biased by force of gravity for vertical translation movement to said lowermost position."
  • The locking swing plate is "positively retained in said lowermost position by the gravity biasing force."
• Independent Claim 10 Essential Elements:
  • A mounting plate with a first receiver wall of varying height, including a "first major rest" and a "declining slide surface."
  • A locking swing plate configured for pivoting and translation movement.
  • The locking swing plate is "positively biased by force of gravity for vertical translation movement."
  • The locking swing plate is "positively retained in said lowermost position by the gravity biasing force."
• The complaint notes that Plaintiffs reserve the right to identify additional grounds for non-infringement as the case proceeds Compl. ¶37

III. The Accused Instrumentality

Product Identification

• The "Home Security Door Lock" sold by Plaintiffs on Amazon under the "EverPlus" brand and ASIN B07HC3M9HH Compl. ¶14 Compl. ¶15

Functionality and Market Context

• The accused product is a door reinforcement lock for inward-swinging doors Compl. ¶14
• The complaint alleges, by referencing the Amazon product page, that the product has a "spring-loaded design" Compl. ¶16 Compl. ¶35 Its operation is described as requiring a user to slide the lock away from its base plate and pull outward to open Compl. ¶16
• The complaint alleges the product has been sold for "several years," with a launch date on Amazon of October 20, 2018 Compl. ¶15 This long-standing market presence is central to Plaintiffs' invalidity allegations Compl. ¶40

IV. Analysis of Infringement Allegations

This is a declaratory judgment action where Plaintiffs allege non-infringement. The table below summarizes Plaintiffs' allegations regarding how their product's functionality differs from the patent's claim requirements.

No probative visual evidence provided in complaint.

'993 Patent Infringement Allegations

Claim Element (from Independent Claim 1)	Plaintiff's Alleged Product Functionality (Denying Infringement)	Complaint Citation	Patent Citation
a locking swing plate configured to translate along a hinge pin vertical axis between an uppermost vertical position and a lowermost vertical position	Plaintiffs allege their product "does not include a locking swing plate that translates along a hinge pin vertical axis between an uppermost and a lowermost vertical position, as the claims require."	¶33	col. 14:39-43
a locking swing plate that is biased by the force of gravity toward the lowermost position and retained by gravity in the lowermost locked position	Plaintiffs allege their product "does not include a locking swing plate that is biased and retained in a lowermost locked position by the force of gravity." The product is instead described as having a "spring-loaded design."	¶35	col. 14:59-65
a specific receiver and locking channel structure, including first receiver ears, first receiver bays, a declining slide surface, and a locking channel...	Plaintiffs allege their product "does not include the claimed first receiver ears, first receiver bays, declining slide surface, locking channel, or any structure that retains a locking swing plate in a lowermost locked position by the force of gravity."	¶37	col. 13:3-65

• Identified Points of Contention:
  • Functional Mismatch: A central question is whether the accused product's "spring-loaded design" Compl. ¶35 is functionally and legally distinct from the claim requirement of a device "biased by the force of gravity" '993 Patent, cl. 1 The complaint frames this as a material difference Compl. ¶35
  • Structural Mismatch: The complaint raises a question of structural non-equivalence by asserting that the accused product lacks the specific "receiver and locking channel structure" Compl. ¶37 and a plate that "translates along a hinge pin vertical axis" Compl. ¶33 as recited in the claims. The court may need to determine if the accused product's components perform the same function in the same way to achieve the same result.

V. Key Claim Terms for Construction

• The Term: "biased by the force of gravity"
• Context and Importance: This term is critical because the Plaintiffs explicitly contrast it with their product's "spring-loaded design" Compl. ¶35 The outcome of the infringement analysis may depend heavily on whether a spring-loaded mechanism can be considered "biased by the force of gravity" or if the claim is limited exclusively to mechanisms where gravity is the sole or primary biasing force. Practitioners may focus on this term because it appears to be a clear point of technical dispute between the patented invention and the accused product.
• Intrinsic Evidence for Interpretation:
  • Evidence for a Broader Interpretation: The patent does not appear to provide significant language supporting a broad interpretation that would encompass non-gravity forces like springs. The focus is consistently on gravity. A party arguing for a broader scope might be limited to general arguments about the term's plain and ordinary meaning, which may be a difficult position.
  • Evidence for a Narrower Interpretation: The patent repeatedly and explicitly recites this limitation. The abstract states the "locking swing plate [is] biased by force of gravity to a lowermost position" '993 Patent, abstract Claim 1 requires the plate to be "positively biased by force of gravity" and "positively retained... by the gravity biasing force" '993 Patent, cl. 1 The detailed description also notes that in the locking position, the plate is "biased by force of gravity to a lowermost position" '993 Patent, col. 2:28-29 This consistent and specific language may support a narrow construction limited to gravity-actuated mechanisms.

VI. Other Allegations

• Indirect Infringement: The complaint seeks a declaration of non-infringement both directly and indirectly Compl. ¶48 While the complaint does not contain affirmative allegations of inducement or contributory infringement, it does describe the enforcement email from Defendants Compl. ¶¶22-28 This communication establishes that Defendants provided Plaintiffs with actual notice of the patent, a key element for any potential future claims of indirect infringement should infringement be found.
• Willful Infringement: The complaint does not mention willfulness. However, the Defendants' enforcement email Compl. ¶22, which allegedly put Plaintiffs on notice of the '993 Patent, would be a central piece of evidence in any future allegation by the Defendants of post-notice willful infringement.

VII. Analyst's Conclusion: Key Questions for the Case

This declaratory judgment action appears to center on two main axes of dispute, one related to infringement and the other to validity.

• A core infringement question will be one of technical and definitional scope: can the claim limitation "biased by the force of gravity" be construed to read on a device described as having a "spring-loaded design"? The case may turn on whether the patent's repeated emphasis on gravity precludes infringement by a product that may use a different physical force for its operation.
• A key validity question will be one of prior public use: does Plaintiffs' allegation that their accused product was on sale since October 2018 Compl. ¶15-more than a year before the patent's earliest priority date of November 2021-create an invalidating on-sale bar under 35 U.S.C. § 102? The court will likely have to resolve the tension in Defendants' position, as Plaintiffs argue that any claim construction broad enough to find infringement would necessarily render the claims invalid over the prior public sale of the same product Compl. ¶41