Product design question

Design a fire alarm system for the deaf.

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What this question tests

Accessibility-focused safety product design, requiring alternate sensory channels to replace the missing auditory alert.

Identify the requirement: replace the auditory alarm with equally reliable visual and tactile alerts, especially while the user is asleep, the highest-risk scenario.
Design the waking alert: a bed-shaker under the mattress or pillow paired with strobing lights, since a sleeping user can't rely on a visual-only cue.
Design the awake-state alert: strong strobe lighting throughout the home, plus a smartwatch vibration alert for mobility around the house.
Add a connected layer: push notifications to a phone or smartwatch, and optionally auto-alert a designated emergency contact, since the user can't hear shouted warnings during evacuation.
Define success as alert-response time benchmarked against hearing users, and false-alarm rate as a guardrail against alert fatigue.

Specifically solves the hardest case, alerting someone asleep, with a bed-shaker, not just strobe lights which fail with eyes closed.
Layers multiple redundant channels, tactile, visual, connected, rather than relying on a single modality.
Defines a response-time benchmark against hearing users, directly measuring whether the design closes the safety gap.

Designing only visual or strobe alerts, missing that strobes fail while asleep, the highest-stakes scenario.
No success metric tied to an actual safety outcome, leaving effectiveness unproven.

How would you ensure the device works during a power outage, when fires are often more likely?
How would you test real-world response time with deaf users?