Low-Power Precision: Why the Federal Circuit Saved Google’s Hotword Patents

In the world of voice-activated technology, efficiency and coordination are everything. If you say "Hey Google" or "Hey Siri" in a room full of connected smart appliances, you only want the intended device to answer—not your phone, tablet, and smart speaker all at once. Solving this problem requires clever engineering, but protecting those solutions requires precise claim drafting and rigorous scrutiny at the Patent Trial and Appeal Board (PTAB).

A recent decision from the U.S. Court of Appeals for the Federal Circuit (CAFC) highlights just how critical the exact timing of device power states can be when defending your intellectual property.

The image above illustrates the core architecture of modern voice-controlled systems, which constantly run in a background "listening" state while waiting to trigger interactive features. In Google LLC v. Sonos, Inc. (decided June 9, 2026), the Federal Circuit reversed two PTAB decisions that had invalidated Google’s patents for "hotword" suppression improvements. The case serves as an excellent reminder of the high evidentiary bar required to prove anticipation in administrative patent challenges.

I. The "Hotword" Conflict

Google’s U.S. Patent Nos. 10,134,398 and 10,593,330 focus on preventing multiple nearby devices from triggering simultaneously. When a hotword is detected, the system ensures the intended device reacts while suppressing responses from surrounding devices.

Sonos challenged these patents via inter partes review (IPR)—an administrative proceeding before the USPTO used to challenge the validity of an issued patent. The PTAB initially sided with Sonos, ruling that Google's independent claims were anticipated by an older prior art patent reference named Rosenberger. Crucially, the Board found that Rosenberger disclosed a system that exchanged weighted signals (the claimed messages) to negotiate which device should respond while those devices remained in a low power mode.

II. The Federal Circuit Demands Substantial Evidence

On appeal, CAFC Chief Judge Moore took a magnifying glass to the Board’s interpretation of the prior art. Google argued that the PTAB’s conclusion was entirely unsupported by substantial evidence, and the Federal Circuit agreed.

The breakdown boiled down to a strict reading of Rosenberger's column 8:

• What the PTAB thought: The Board, relying heavily on expert testimony from Sonos, concluded that the prior art device exchanged coordination messages while remaining in its low-power "listening" state.

• What the Prior Art actually said: The Federal Circuit found that Rosenberger explicitly described embodiments where, upon detecting a spoken command, the devices exit the low-power mode before calculating and exchanging weighted signals.

Because the prior art required the devices to wake up prior to communicating, it failed to disclose the specific limitation of exchanging messages while in a low power mode.

Sonos attempted to patch this evidentiary gap with alternative theories—arguing that a change in a status light or the term "wakes up" could be read flexibly to fit the agreed-upon construction of "low power mode" (an operating state where power is conserved). However, the CAFC firmly rejected these arguments, noting that the Board failed to make actual factual findings to back up those leaps in logic. The court reversed the findings of unpatentability and remanded the case back to the Board.

III. Wood Phillips Takeaway

For software and microprocessor developers, this decision underscores two vital strategic realities:

1. Precision in the Prosecution Phase: When drafting claims involving state-based logic (like power modes, sleep cycles, or network states), the relationship between the timing of an action and the state of the device is a powerful tool to distinguish your invention from the prior art.

2. Holding the Board Accountable: Expert testimony cannot substitute for what a prior art document actually discloses. On appeal, the Federal Circuit will not permit the PTAB to rewrite a reference's text to achieve an anticipation finding.