Your phone only rings for people you know.
Sentinela is an unknown-call blocker for Android. The decision happens inside your device, in a fraction of a second, looking only at your contacts and your personal list — no server, no sign-up and no telemetry.
Google Play release in progress. In the meantime, the full source code is already open under the MIT license.
- No ads
- No telemetry
- No sign-up
- No internet permission
What happens to each call
Every origin follows the policy you choose: ring, silence or block. Numbers appear masked in alerts and technical logs.
How screening works
Four steps, all inside the device. None of them depends on a network — the app works the same in airplane mode.
The call comes in
Android hands the call to Sentinela before the first ring, through the system's official screening role.
Local lookup
The engine compares the number against your contacts and your personal whitelist. Nothing leaves the device, because there is nowhere for it to go.
Decision
Ring, silence or block — according to the policy you set for each origin. The answer to the system is single and immediate.
Optional record
If you want, the block goes into a local history, kept for the retention period you choose. If you don't, nothing is stored.
Two protection modes
Filter mode handles the common case without touching your phone app. Dialer mode goes further — and it is optional, reversible and always your choice.
Filter mode (default)
Sentinela takes on Android's call screening role and works in the background. Your phone app stays the one you already use; saved contacts keep ringing normally. This is the recommended mode for most people.
Dialer mode (optional)
Sentinela becomes the default phone app, with its own call and dialing screens. That unlocks policies for specific contacts. You can go back to your previous dialer at any time, from Android's own picker.
What stays under your control
No setting is hidden behind a subscription, an account or an ad.
- Personal whitelist — add numbers that may always ring, with a description, search and file export/import.
- Policy per origin — separate rules for contacts, whitelist, unknown and private numbers.
- Blocking mode — block outright or just silence, with no call screen.
- Opt-in notification — off by default; you decide whether you want to know who was turned away.
- History retention — never store, 7, 30, 90 days or until you delete it.
- Clear everything — one button wipes whitelist, history and settings. Uninstalling removes the rest.
Privacy is not a promise, it is architecture
The strongest guarantee that an app does not send your data anywhere is that it cannot send it. That is how Sentinela was built.
No internet permission
The app declares no network access. Technically there is no way to send anything out — not by mistake, not through a silent library update.
Contacts in memory only
Your address book is read at the moment of the call. Contact name, photo and number are never written to a database, a log or a backup.
No telemetry and no ads
No analytics SDK, no ad network, no advertising identifier, no event sent to third parties.
Outside automatic backup
The local database (whitelist, history and settings) is excluded from Google backup and from device-to-device transfer.
Never a full number in a log
Technical logs and notifications use a mask — +55 11 9****-1234. The full number stays only in the local database, if you turn history on.
Auditable code
MIT license, public repository. Anyone can check whether what is written here is what the app does.
Limitations we tell you up front
A blocking app that promises everything is lying somewhere. These are the platform's real boundaries.
- Traditional phone calls only. Calls from WhatsApp, Telegram and other voice-over-internet apps do not go through Android's call filter and are not affected.
- The system log still exists. Hiding a blocked call from the phone's native call history is not possible for third-party apps.
- Manufacturers vary. Some brands add their own call and battery management layers; behaviour may differ between devices.
- No filter is infallible. Sentinela decides from what is on your device — anyone who is neither in your contacts nor on your whitelist is treated as unknown, including a call you were expecting.
Technical sheet
| Platform | Android 10 (API 29) or higher — required by the call screening role |
|---|---|
| App identifier | com.sierratecnologia.sentinela |
| License | MIT — free to use, study and modify |
| Price | Free, with no in-app purchases and no subscription |
| Language | Portuguese (Brazil) |
| Source code | github.com/ricardosierra/sentinela |
| Maintained by | Sierra Tecnologia and Rica Soluções |
Questions about Sentinela?
Talk to us. And if your company needs a privacy solution or a custom app built with the same rigour, the conversation starts the same way: an assessment, at no cost.