Hush

A small, open-source, offline call blocker for Android. You can block numbers by pattern, so a company that rotates through +91 80 4718 xxxx can't reach you.

• No internet permission. The manifest strips INTERNET, so the app cannot send data anywhere.
• No accounts, analytics, ads, crowd-sourced spam lists or caller-ID lookups.
• Rules and history are stored in the app's private storage and excluded from Google backup. You can export rules to a JSON file yourself.

Rule types

Type	Example	Matches
Exact number	+91 98765 43210	That number, written either way (098765 43210 too)
Starts with	+91 80 4718	Every number beginning with those digits
Pattern	+91 80 47## 12##	# or ? = one digit, * = any run of digits
Regex	\+91(80|22)4718\d{4}	A Java regex that must match the whole number

Each rule does one of three things:

• Block: reject the call.
• Silence: let it ring with no sound, so it still shows up as a missed call.
• Always allow: an exception that beats every block rule. For example, block +91 80 4718 but allow +91 80 4718 0000 because it's your bank.

Set your country calling code in Settings. With it set, a rule written as 080 4718 also matches a call from +91 80 4718 …, and the reverse.

The Rules tab has a Test a number box that shows which rule, if any, would catch a number.

Writing a rule from a call you got

The Blocked tab lists every call Hush screened, including the ones that rang through. Tap Block… on one and the rule editor opens with that number filled in — then you decide the pattern: trim the last digits for a Starts with rule, or replace them with # for a Pattern rule. Hush never guesses a pattern for you.

How it works

• ScreeningService is an Android CallScreeningService. After you make Hush the phone's call-screening app (the app asks on first launch), Android asks it about every incoming call. The decision comes only from your local rules.
• core/Rules.kt holds the matching engine. It's plain Kotlin with no Android dependencies, and it's covered by app/src/test/.../RuleEngineTest.kt.
• The Contacts tab turns on Android's built-in "send to voicemail" flag for saved contacts. This is needed because Android doesn't pass calls from saved contacts to screening apps.
• Settings has Block everyone not in my contacts for when you want the opposite default. "Always allow" rules still get through it.

Limitations

• Needs Android 10 (API 29) or newer.
• Only one app can hold the call-screening role at a time. If you use Truecaller or a similar app, this replaces it.
• SMS blocking isn't included. Android only lets the default SMS app filter messages.
• Pattern rules don't apply to saved contacts (see the Contacts tab above).
• The call history only contains calls Android handed to the screening service, so calls from saved contacts never appear there.

Build

You need JDK 17 and the Android SDK (Android Studio is the easiest way to get it).

./gradlew testDebugUnitTest assembleDebug
# APK: app/build/outputs/apk/debug/app-debug.apk
adb install app/build/outputs/apk/debug/app-debug.apk

The GitHub Actions workflow in .github/workflows/build.yml runs the tests and uploads a debug APK on every push.

License

Hush is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License v3.0 as published by the Free Software Foundation.