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2026-03-20 | 🔒☀️ Keeping Screens Awake During TTS Playback

🧑‍💻 Author’s Note

• 🎯 Goal: Prevent phone screens from locking while the TTS player reads article content aloud
• 🔧 Approach: Screen Wake Lock API with visibilitychange re-acquisition — zero dependencies
• 🧪 Testing: All 118 existing TTS tests pass, site builds successfully
• 📐 Principles: Progressive Enhancement, Zero Dependencies, Graceful Degradation

🎭 The Problem: Pocketed Silence

Picture this: you’re listening to a long article through the TTS player on your phone. You set it down, or slip it into your pocket. Thirty seconds later — silence. The screen locked, the browser suspended, and the speech synthesis died mid-sentence.

The Web Speech API’s SpeechSynthesis runs in the browser’s main thread. When the OS locks the screen, the browser gets backgrounded and speech stops. On mobile devices with aggressive power management, this happens quickly — often within 30 seconds of inactivity.

🏗️ The Research: Four Candidate Approaches

Before writing a single line of code, I evaluated four distinct strategies:

Plan 1: Screen Wake Lock API Only

The Screen Wake Lock API (navigator.wakeLock.request('screen')) is a W3C standard designed exactly for this use case.

Aspect	Assessment
Dependencies	Zero — pure browser API
Battery impact	Minimal — tells OS to keep screen on, no CPU tricks
Browser support	Chrome 84+, Firefox 126+, Safari 16.4+ (95%+ mobile users)
Risk	No fallback for very old browsers

Plan 2: NoSleep.js Library

The NoSleep.js library plays a hidden, looping video element to trick the OS into thinking media is active.

Aspect	Assessment
Dependencies	Adds npm package
Battery impact	Higher — hidden video consumes CPU
Browser support	Broader legacy support
Risk	Autoplay restrictions increasingly block it; semi-abandoned project

Plan 3: Silent Audio Element Fallback

Play a tiny, silent, looping audio file alongside the TTS.

Aspect	Assessment
Dependencies	Requires bundling an audio asset
Battery impact	Low-moderate
Browser support	Broad
Risk	TTS already IS audio via SpeechSynthesis — redundant layer

Plan 4: Wake Lock API + Visibility Re-acquisition ✅

Use the Wake Lock API with a visibilitychange event handler to automatically re-acquire the lock when the user returns to the tab.

Aspect	Assessment
Dependencies	Zero
Battery impact	Minimal
Browser support	Same as Plan 1 (excellent)
Edge case handling	Re-acquires after tab switch — the critical mobile scenario

🎯 The Decision: Plan 4

Plan 4 won decisively. Here’s the reasoning:

1. Right tool for the job — the Screen Wake Lock API was literally designed to prevent screen sleep during active content consumption
2. Zero dependencies — aligns with the codebase’s pattern of self-contained inline scripts with no external libraries
3. The visibility handler is essential — browsers release wake locks when tabs go to background; re-acquiring on return is the difference between “works sometimes” and “works reliably”
4. Graceful degradation — if the API isn’t available, the TTS player works exactly as before; no errors, no broken UI

🔧 The Implementation: ~30 Lines of Surgical Code

The entire feature fits into three functions added to tts.inline.ts:

acquireWakeLock()   — request screen wake lock  
releaseWakeLock()   — release it (idempotent, error-safe)  
onVisibilityChange() — re-acquire if tab becomes visible while playing  

Integration Points

The wake lock lifecycle mirrors the TTS playback lifecycle:

TTS Event	Wake Lock Action
Play / Resume	acquireWakeLock()
Pause	releaseWakeLock()
Stop (end of article)	releaseWakeLock()
Tab becomes visible + playing	acquireWakeLock()
SPA navigation cleanup	releaseWakeLock() + remove listener

Key Design Decisions

No separate module — Wake lock is a browser API (like SpeechSynthesis itself). It belongs in tts.inline.ts alongside the other browser-dependent code, not in tts.utils.ts which is reserved for pure functions.

Fire-and-forget async — acquireWakeLock() is async but we don’t await it in speakFrom(). The wake lock request runs concurrently with speech start. If it fails (low battery, permissions policy), speech continues normally.

Idempotent release — releaseWakeLock() handles the case where the sentinel was already released (by the OS or a previous call) without throwing.

Release event listener — When the OS releases the wake lock (e.g., low battery), the release event nulls out our sentinel reference so we don’t try to release it again.

📊 Browser Support

Browser	Minimum Version
Chrome Android	84+
Firefox Android	126+
Safari iOS	16.4+
Samsung Internet	14+
Edge Android	84+

This covers effectively all modern mobile browsers. The remaining ~5% of users on older browsers simply get the existing behavior — the TTS player works, but the screen may lock during playback.

🧠 Lessons Learned

1. Research before code — evaluating 4 approaches before coding meant the implementation was obvious and took minutes
2. The best abstraction is often the simplest — 30 lines of well-placed code beat a library dependency every time
3. Progressive enhancement is the web’s superpower — feature detection ("wakeLock" in navigator) means zero risk of breaking existing functionality
4. Lifecycle symmetry is elegant — acquire on play, release on stop maps perfectly onto the existing TTS state machine