PrivacyScreen

A Swift Package library that simulates hardware-level privacy screen protection using ARKit face tracking and CoreMotion sensor fusion. When someone looks over your shoulder, your sensitive content blurs. When a threat clears, it fades back.

demo.mp4

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What It Does

Most privacy screen protectors are physical filters that dim your display. PrivacyScreen does it in software by watching for three threat signals in real time:

• Second face — ARKit detects someone else looking at your screen
• Gaze deviation — you look away, suggesting you're handing the device over or distracted
• Device tilt — the phone tilts past a natural holding angle, or rotates suddenly (snatch detection)

These signals are fused into a ThreatLevel that drives progressive content blurring without ever blocking the UI.

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Expected Behavior

Threat levels

.clear      Normal use. All content visible.

.cautious   Slight shoulder-surfing risk.
            High-sensitivity content blurs (balances, card numbers, CVV).

.threatened Elevated risk — gaze drifted, tilt detected.
            Medium-sensitivity content also blurs (names, dates).

.locked     Instant lock — second face detected, or rapid tilt (snatch).
            Full-screen privacy shield activates. Low-sensitivity
            content (merchant names) hidden too.

Progressive blur — what you see

Normal view                  .cautious                    .locked
┌─────────────────────┐      ┌─────────────────────┐      ┌─────────────────────┐
│ Total Balance       │      │ Total Balance       │      │░░░░░░░░░░░░░░░░░░░░░│
│                     │      │                     │      │░░░░░░░░░░░░░░░░░░░░░│
│   $184,229.47       │  →   │   ███████████       │  →   │░░░░░░░░░░░░░░░░░░░░░│
│   +$2,847.33        │      │   ████████          │      │░░░  Privacy Mode ░░░│
│   ▁▃▅▆▇▇▇▇▇▇▇▇▇     │      │   █████████████     │      │░░░    Active     ░░░│
│                     │      │                     │      │░░░░░░░░░░░░░░░░░░░░░│
│ Primary Checking    │      │ Primary Checking    │      │░░░░░░░░░░░░░░░░░░░░░│
│ ....4281            │      │ ....4281            │      │░░░░░░░░░░░░░░░░░░░░░│
│ $42,847  +$1,247    │      │ ██████████  ██████  │      │░░░░░░░░░░░░░░░░░░░░░│
└─────────────────────┘      └─────────────────────┘      └─────────────────────┘
  Touch passes through          Touch passes through          Touch passes through

The overlay always uses .allowsHitTesting(false) — the UI remains fully interactive under the blur.

.clear  →  .cautious  →  .threatened  →  .locked

Sensitivity mapping

Content	Sensitivity	Blurs at
Account balances, card numbers, CVV	.high	.cautious
Names, account numbers, dates	.medium	.threatened
Merchant names	.low	.locked

Power states

PrivacyScreen adapts its power draw based on how actively the device is being used:

  pickup
────────▶ ACTIVE (180mW)   accel 30Hz, ARKit continuous 60fps
              │
   still 8s   │
              ▼
          IDLE (30mW)      accel 15Hz, ARKit 0.5s bursts every 3s (~17% duty)
              │
  still 30s   │
              ▼
        DORMANT (5mW)      accel 5Hz, ARKit off (wake-on-motion)

  threat ≥ .threatened (from any state)
────────▶  ALERT (180mW)   same as ACTIVE; exits after threat clears + 5s cooldown
                           ──▶ ACTIVE

Idle mode saves ~83% power vs always-on by duty-cycling ARKit at 17%.

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Library Integration

Swift Package Manager

// Package.swift
.package(path: "../PrivacyScreen")  // local

// or from a remote URL:
.package(url: "https://github.com/abhay/PrivacyScreen", from: "0.1.0")

Setup

import PrivacyScreen
import SwiftUI

@main
struct MyApp: App {
    @StateObject private var privacyManager = PrivacyManager()
    @StateObject private var powerThrottler = PowerThrottler()

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(privacyManager)
                .environmentObject(powerThrottler)
                .onAppear {
                    // PowerThrottler owns the CMMotionManager — pass externalMotion: true
                    privacyManager.startMonitoring(externalMotion: true)
                    powerThrottler.attach(to: privacyManager, arSession: privacyManager.arSession)
                    powerThrottler.start()
                }
        }
    }
}

Important: iOS enforces a single CMMotionManager per app. PowerThrottler owns it and forwards data via processMotionFromThrottler(_:). Never create a second instance.

Mark sensitive content

// Balances, card numbers, CVV — blur at .cautious
Text(formatCurrency(account.balance))
    .privacySensitive(level: .high)

// Names, dates — blur at .threatened
Text(account.holderName)
    .privacySensitive(level: .medium)

// Merchant names — blur at .locked only
Text(transaction.merchant)
    .privacySensitive(level: .low)

Add the shield overlay

ZStack {
    MyContentView()
    PrivacyShieldOverlay()  // full-screen lock at .locked
}

Optional: debug overlay

if privacyManager.showDebugOverlay {
    PrivacyDebugOverlay()  // live sensor readouts
    PowerDebugView()       // power state machine
}

Threat level colors

ThreatLevel exposes a color: Color property for building your own indicators:

Circle()
    .fill(privacyManager.threatLevel.color)
// .clear → .green, .cautious → .yellow, .threatened → .orange, .locked → .red

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VaultDemo

A Mercury/Revolut-inspired finance app (all data hardcoded) that shows PrivacyScreen on realistic UI.

Screens

Tab	Content	Sensitive fields
Dashboard	Total balance, sparkline chart, account list, recent transactions	Balance, daily change, account numbers
Accounts	Per-account balance cards with daily P&L	Balances, full account numbers
Activity	Transaction history with merchant, category, date	Amounts, dates, merchant names
Cards	Full card face with number, expiry, CVV	Card number, CVV, cardholder name, expiry
Settings	Privacy toggles, tilt/gaze sensitivity sliders, "Simulate Threat" button	—

Cards

Each card carries a CardTheme that controls its gradient:

• .blue — blue-to-violet gradient (Visa credit card)
• .slate — dark charcoal gradient (Mastercard debit)

Simulator testing

ARKit face tracking requires a physical device with a TrueDepth camera (iPhone X or later). On simulator:

• Face tracking is disabled; tilt detection still works
• Use Settings → Simulate Threat to force .locked state for 3 seconds and see the full overlay

Demo mode

Launch with -demo to run a scripted walkthrough of all threat levels with captions — useful for recording videos:

xcrun simctl launch booted com.vaultdemo.app -demo

Launch with -screenshots for the same sequence without captions (clean screenshots).

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Architecture

ARKit face anchors ──┐
                     ├──→ ThreatState (pure scoring, fully testable)
CMMotionManager ─────┘         │
(owned by PowerThrottler)      ↓
                         PrivacyManager (@MainActor, publishes threatLevel)
                               │
                    ┌──────────┴──────────┐
                    ↓                     ↓
         PrivacySensitiveModifier   PrivacyShieldOverlay
         (blur per sensitivity)     (full lock at .locked)

Scoring

secondFaceDetected          → instant .locked
deviceTiltRate > 120°/s     → instant .locked (snatch)

primaryFaceLost             → +2
gazeDeviation > 0.5 rad     → +2
gazeDeviation > 0.3 rad     → +1
abs(tiltAngle) > 40°        → +2
abs(tiltAngle) > 25°        → +1

score 0 → .clear
score 1 → .cautious
score 2 → .threatened
score 3+ → .locked

Escalation is immediate (1–2 frames). De-escalation requires all 8 frames in the smoothing window to be below the current level (~133ms hysteresis).

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Requirements

• iOS 17+
• Xcode 16+
• TrueDepth camera for ARKit face tracking (iPhone X or later); falls back to accelerometer-only on older devices and simulator

Development

# Build the library
swift build --sdk "$(xcrun --sdk iphonesimulator --show-sdk-path)" \
  -Xswiftc "-target" -Xswiftc "arm64-apple-ios17.0-simulator"

# Run tests (29 ThreatState unit tests)
xcodebuild test -scheme PrivacyScreen \
  -destination 'platform=iOS Simulator,name=iPhone 16' -quiet

# Build VaultDemo
xcodebuild build -project Example/VaultDemo/VaultDemo.xcodeproj \
  -scheme VaultDemo -destination 'platform=iOS Simulator,name=iPhone 16' -quiet

# Lint and format
swiftlint lint Sources/ Tests/ Example/
swiftformat --lint Sources/ Tests/ Example/

# Auto-fix
swiftformat Sources/ Tests/ Example/
swiftlint lint --fix Sources/ Tests/ Example/

Pre-commit hooks (SwiftFormat + SwiftLint) and pre-push hooks (tests) run automatically via lefthook.