A minimalist Android app that blocks distracting apps using NFC tags and scheduled modes. Built to add physical friction between you and your phone.
Google Play · Releases · Website
Concept
nfcGuard forces you to physically interact with an NFC tag to unlock blocked apps. Place your tag somewhere inconvenient — your kitchen, gym bag, a friend's house — and you'll think twice before mindlessly opening Instagram.
Flow: Create a mode → select apps to block (or allow) → optionally link NFC tags → optionally set a schedule → activate → stay focused → tap your NFC tag when you actually need access.
If no NFC tag is linked to a mode, any NFC-capable object (smartwatch, headphones, transit card) can deactivate it.
Screenshots
Main Screens
Overlay in Action
Features
Modes
Two blocking strategies:
- Block Selected — block specific distracting apps while everything else remains accessible
- Allow Only — block everything except a whitelist of essential apps
Each mode can have multiple NFC tags linked to it. Each tag can be individually configured:
- Permanent unlock — tapping the tag fully deactivates the mode until the next scheduled activation
- Temporary unlock — tapping the tag unlocks for a configurable duration (e.g. 5 minutes), after which the mode automatically reactivates
This lets you set up different levels of access. For example, keep one tag at home for full unlock and another at work that only gives you 5 minutes — enough to quickly check something without falling down a scroll hole.
Schedules
Automate mode activation with flexible scheduling:
- Per-day time configuration (different start/end times for each day of the week)
- Optional automatic deactivation at end time
- Multiple modes can be linked to a single schedule
- Visual status badges: ACTIVE when a schedule is running, DEACTIVATED when dismissed early via NFC
NFC Integration
- Register physical NFC tags by tapping them to your device
- Link multiple tags to a single mode, each with its own unlock behavior
- Configure per-tag unlock duration (permanent or temporary with a time limit)
- Modes with linked tags require one of those specific tags — other tags won't work
- Wrong-tag feedback when an incorrect tag is scanned
Settings & Permissions
Accessible via the gear icon on the home screen:
- Permission status — see which permissions are granted, tap to open the relevant system settings
- Export/Import — back up your entire configuration (modes, schedules, NFC tags) in JSON or YAML format
- Export to share configs between devices or keep a backup
- Import with two strategies: Replace (overwrite everything) or Merge (add non-duplicate items)
- Pause App reminder — quick link to disable Android's "Pause app if unused" setting
Emergency Reset
If you lose your NFC tag:
- Tap the delete icon on the home screen
- Complete the safety flow (90-second cooldown + confirmation text)
- Select which tags you lost
- All modes are deactivated and selected tags are removed — your configurations stay intact
Technical Details
Requirements
- Android 8.0+ (API 26)
- NFC hardware (for NFC unlock features)
- Permissions:
- Usage Access — detect which app is in the foreground
- Display Over Apps — show the block overlay
- Battery Optimization exemption — ensure reliable background operation
- Disable "Pause app if unused" — prevent Android from hibernating nfcGuard
Architecture
Kotlin + Jetpack Compose, organized as two Gradle modules with strict layering:
:domain Pure Kotlin (no Android imports — compiler-enforced).
AppState + the four logic objects: NfcUnlockLogic,
ScheduleTransitions, ModeActivationLogic, BlockDecider.
78 unit tests run as plain JVM, no emulator needed.
:app Everything else. Sub-packaged by layer:
ui/ data/ service/ receiver/ sync/ widget/
Inside :app, the layers flow in one direction — Domain → Data → Side effects → Service / UI — with one owner per concern:
AppStateRepositoryis the single owner of persisted state (guardian_prefs:app_state). Every mutation goes throughsuspend update(transform: (AppState) -> AppState), mutex-guarded. Exactly one file in the codebase references that storage key.StateSynceris the single dispatcher for platform side effects. The repo auto-invokes it on every successful write, and it does the right thing: restartBlockerServicewith the new params (or stop it entirely if nothing's left to do), reschedule schedule alarms, diff per-mode timed alarms, refresh widgets. There are exactly twoBlockerService.start(...)callsites and both are insideStateSyncer.GuardianViewModelis a thin orchestrator over the domain. Mutating methods are 4-6 lines each — pattern-match on a sealed result from a domain logic object, then callmutate { … }which goes through the repo.BlockerServiceis a lifecycle host over three collaborators:ForegroundAppDetector(dual-source detection),BlockDecider(pure decision), and anEnforcerinterface with two implementations (OverlayEnforcerandForceCloseEnforcer).
Persistence is kotlinx.serialization over SharedPreferences. Scheduling is AlarmManager with setExactAndAllowWhileIdle. Alarms, boot, and service restarts are handled by thin BroadcastReceiver adapters that read repo.current and call StateSyncer.sync(context, state).
How Blocking Works
A foreground service (BlockerService) polls the current foreground app every ~500ms and uses one of two strategies to block, picked per tick based on whether the Accessibility Service permission is granted:
- Overlay strategy (accessibility off): a full-screen
SYSTEM_ALERT_WINDOWis drawn over the blocked app. The user can tap aGUARDIANbutton to open the app, or scan an NFC tag to unlock. - Force-close strategy (accessibility on): the user is sent to HOME via the Accessibility Service (bypasses MIUI's background-activity-start restrictions), the blocked app's background processes are killed, and a brief toast is shown. A 3-second cooldown prevents spamming HOME while accessibility events catch up.
Foreground-app detection is dual-source for reliability: the Accessibility Service event timeline (primary, required on Pixel and some Samsung devices where UsageStatsManager misreports recents→app transitions), with UsageStatsManager.queryEvents and queryUsageStats as fallbacks.
Whether the overlay strategy or force-close strategy is right for a given device depends on quirks — overlay races badly with the Accessibility Service on Samsung; force-close needs the Accessibility Service for the HOME action to be reliable on MIUI. The runtime selection per tick covers both.
Installation
Google Play: Download from Play Store
APK: Go to the Releases page and download the latest APK. Install it on your device, grant the necessary permissions, and configure your modes and schedules.
Manual Installation
- Clone the repository
- Open in Android Studio, or build from the command line:
./gradlew :app:assembleDebug # debug APK → app/build/outputs/apk/debug/ ./gradlew :app:installDebug # install on attached device ./gradlew :domain:test # pure-JVM unit tests (fast, no Android SDK) ./gradlew test # both modules
- Run on a physical device — NFC requires real hardware; emulator support is unusable.
Configuration for Custom ROMs
Some manufacturers (Xiaomi, Samsung, Huawei) aggressively kill background services. After installation:
- Settings → Apps → nfcGuard — disable "Pause app activity if unused"
- Enable Autostart if available (MIUI, ColorOS)
- Set battery optimization to Unrestricted / No restrictions
- On MIUI: add nfcGuard to the Lock screen cleanup whitelist
Export Format Examples
JSON
{
"version": 1,
"modes": [
{
"id": "abc-123",
"name": "Work Focus",
"blockedApps": ["com.instagram.android", "com.twitter.android"],
"blockMode": "BLOCK_SELECTED",
"nfcTagIds": ["tag-001", "tag-002"]
}
],
"schedules": [],
"nfcTags": [
{
"id": "tag-001",
"name": "Home tag",
"unlockDurationMinutes": null
},
{
"id": "tag-002",
"name": "Work tag",
"unlockDurationMinutes": 5
}
]
}YAML
# nfcGuard Configuration Export version: 1 modes: - id: "abc-123" name: "Work Focus" blockMode: BLOCK_SELECTED nfcTagIds: - "tag-001" - "tag-002" blockedApps: - "com.instagram.android" - "com.twitter.android" schedules: [] nfcTags: - id: "tag-001" name: "Home tag" unlockDurationMinutes: null # permanent unlock - id: "tag-002" name: "Work tag" unlockDurationMinutes: 5 # temporary 5-minute unlock
My personal configuration
Click to view my personal configuration
{ "version": 1, "modes": [ { "id": "2fc26ed7-25a2-4696-9d57-c6f0fec210cd", "name": "Daily", "blockedApps": [ "co.hinge.app", "com.reddit.frontpage", "com.spotify.music", "com.zhiliaoapp.musically", "com.google.android.apps.youtube.music", "app.revanced.android.apps.youtube.music", "com.yandex.browser", "app.revanced.android.youtube", "com.instagram.android", ], "blockMode": "BLOCK_SELECTED", "nfcTagId": "0463b1f1220289", }, { "id": "e3a2e7c8-55eb-4d59-8cbf-2ada6dc0ff05", "name": "evening", "blockedApps": [ "co.hinge.app", "app.revanced.android.youtube", "com.yandex.browser", ], "blockMode": "BLOCK_SELECTED", "nfcTagId": "0463b1f1220289", }, ], "schedules": [ { "id": "fd1c04cb-b43e-4f43-961a-313fb5db773f", "name": "morning", "timeSlot": { "dayTimes": [ { "day": 1, "startHour": 0, "startMinute": 0, "endHour": 11, "endMinute": 59, }, { "day": 2, "startHour": 0, "startMinute": 0, "endHour": 11, "endMinute": 59, }, { "day": 3, "startHour": 0, "startMinute": 0, "endHour": 11, "endMinute": 59, }, { "day": 4, "startHour": 0, "startMinute": 0, "endHour": 11, "endMinute": 59, }, { "day": 5, "startHour": 0, "startMinute": 0, "endHour": 11, "endMinute": 59, }, { "day": 6, "startHour": 0, "startMinute": 0, "endHour": 11, "endMinute": 59, }, { "day": 7, "startHour": 0, "startMinute": 0, "endHour": 11, "endMinute": 59, }, ], }, "linkedModeIds": ["2fc26ed7-25a2-4696-9d57-c6f0fec210cd"], "hasEndTime": true, }, { "id": "2e4c179e-bbff-4ba6-8634-3980187f9788", "name": "day ", "timeSlot": { "dayTimes": [ { "day": 1, "startHour": 12, "startMinute": 15, "endHour": 14, "endMinute": 59, }, { "day": 2, "startHour": 12, "startMinute": 15, "endHour": 14, "endMinute": 59, }, { "day": 3, "startHour": 12, "startMinute": 15, "endHour": 14, "endMinute": 59, }, { "day": 4, "startHour": 12, "startMinute": 15, "endHour": 14, "endMinute": 59, }, { "day": 5, "startHour": 12, "startMinute": 15, "endHour": 14, "endMinute": 59, }, { "day": 6, "startHour": 12, "startMinute": 15, "endHour": 14, "endMinute": 59, }, { "day": 7, "startHour": 12, "startMinute": 15, "endHour": 14, "endMinute": 59, }, ], }, "linkedModeIds": ["2fc26ed7-25a2-4696-9d57-c6f0fec210cd"], "hasEndTime": true, }, { "id": "9b0ff839-eaba-4aa5-a55f-a1873deb6a26", "name": "late day", "timeSlot": { "dayTimes": [ { "day": 1, "startHour": 15, "startMinute": 15, "endHour": 17, "endMinute": 59, }, { "day": 2, "startHour": 15, "startMinute": 15, "endHour": 17, "endMinute": 59, }, { "day": 3, "startHour": 15, "startMinute": 15, "endHour": 17, "endMinute": 59, }, { "day": 4, "startHour": 15, "startMinute": 15, "endHour": 17, "endMinute": 59, }, { "day": 5, "startHour": 15, "startMinute": 15, "endHour": 17, "endMinute": 59, }, { "day": 6, "startHour": 15, "startMinute": 15, "endHour": 17, "endMinute": 59, }, { "day": 7, "startHour": 15, "startMinute": 15, "endHour": 17, "endMinute": 59, }, ], }, "linkedModeIds": ["2fc26ed7-25a2-4696-9d57-c6f0fec210cd"], "hasEndTime": true, }, { "id": "ec2a3b62-8056-404e-9f2c-c5aed210a163", "name": "evening", "timeSlot": { "dayTimes": [ { "day": 1, "startHour": 18, "startMinute": 15, "endHour": 20, "endMinute": 59, }, { "day": 2, "startHour": 18, "startMinute": 15, "endHour": 20, "endMinute": 59, }, { "day": 3, "startHour": 18, "startMinute": 15, "endHour": 20, "endMinute": 59, }, { "day": 4, "startHour": 18, "startMinute": 15, "endHour": 20, "endMinute": 59, }, { "day": 5, "startHour": 18, "startMinute": 15, "endHour": 20, "endMinute": 59, }, { "day": 6, "startHour": 18, "startMinute": 15, "endHour": 20, "endMinute": 59, }, { "day": 7, "startHour": 18, "startMinute": 15, "endHour": 20, "endMinute": 59, }, ], }, "linkedModeIds": ["e3a2e7c8-55eb-4d59-8cbf-2ada6dc0ff05"], "hasEndTime": true, }, { "id": "b7bf3650-a6c9-4cbd-92ca-f9dd77128099", "name": "night", "timeSlot": { "dayTimes": [ { "day": 1, "startHour": 21, "startMinute": 15, "endHour": 23, "endMinute": 59, }, { "day": 2, "startHour": 21, "startMinute": 15, "endHour": 23, "endMinute": 59, }, { "day": 3, "startHour": 21, "startMinute": 15, "endHour": 23, "endMinute": 59, }, { "day": 4, "startHour": 21, "startMinute": 15, "endHour": 23, "endMinute": 59, }, { "day": 5, "startHour": 21, "startMinute": 15, "endHour": 23, "endMinute": 59, }, { "day": 6, "startHour": 21, "startMinute": 15, "endHour": 23, "endMinute": 59, }, { "day": 7, "startHour": 21, "startMinute": 15, "endHour": 23, "endMinute": 59, }, ], }, "linkedModeIds": ["e3a2e7c8-55eb-4d59-8cbf-2ada6dc0ff05"], "hasEndTime": false, }, ], "nfcTags": [{ "id": "0463b1f1220289", "name": "NFC card", "linkedModeIds": [] }], }
License
MIT License
Contributing
Contributions are welcome. Open an issue or submit a pull request.
Acknowledgments
Claude AI was used during the development of this project for writing code and UI design.