Nexus-SecTech Ltd · Android
CallVault
A personal Android call recorder. Records both sides of a call as separate channels, keeps them on your phone, and backs them up to your own Google Drive.
What it does
Both sides, separately
On a phone call your voice and theirs are captured as distinct channels, so you can isolate either one, or listen to both together.
App calls, with caveats
Calls inside a messaging app can be recorded too, as a single mixed track. Tested with two apps, and the weaker of the two routes. See below.
Transcribed on the phone
Speech is turned into text by a model running on the device itself. Nothing is uploaded to transcribe it, and it works offline.
Search what was said
Once a call is transcribed you can find it by a phrase from inside it, not only by a name or a number. Tap a line to jump to that moment.
Verifiable
Every recording is stored with a SHA-256 hash and a sidecar describing the call. It is an audit tool, not a notes app.
Yours alone
No account, no server, no analytics. Backup goes to a folder in your own Drive using the narrowest scope Google offers.
The two kinds of call are not equal
A phone call is captured from the call audio itself, which is why both parties arrive as separate channels at a consistent level. That is the route CallVault was built for and it is the one to rely on.
A call made inside another app is captured differently, and the difference matters. It arrives as one mixed track with no way to separate the two voices, and your own voice is always the louder of the two. How well the other party comes through depends on whether the phone was on speaker or held to the ear: across the calls measured so far the difference was more than thirty decibels, and the quietest was not worth keeping. The player has controls that help with the rest.
It has been confirmed with two messaging apps. CallVault does not keep a list of app names, which is why nothing here is named after a particular app. It notices a call two ways: an app showing an ongoing call notification while the phone line is idle, or the phone switching into the audio mode apps use for calls. The second was added because the second app tested does not label its call as a call, and until then its calls were missed entirely or cut short. That is a fair warning about the rest: each app behaves in its own way, and apps beyond these two have not been tried.
Treat it as a useful addition rather than a substitute. If a call matters, make it a phone call.
Transcription
Any recording can be turned into text, and the model that does it runs on the phone. Nothing is uploaded, no account is involved, and it works with the phone in flight mode. A long call takes a few minutes of the device's own processing time.
A transcript can be searched, and tapping a line jumps the player to that moment. Reference numbers, amounts, dates and commitments are picked out of the text by pattern, which is worth exactly as much as the transcript it came from. Read the transcript, not just the summary.
If a call arrives while a transcription is running, the transcription is abandoned immediately. Recording the call is what this app is for.
How backup works
Backup is off until you choose a Google account. Once enabled, each recording and its
sidecar are uploaded to a CallVault folder in that account's Drive, straight
after the call rather than on a schedule. A phone lost an hour after an important call
should not take the only copy with it.
The app requests a single OAuth scope, drive.file, which grants access only
to files the app itself created. It cannot see anything else in your Drive.
googleapis.com is the only internet destination it contacts.
The law on recording calls varies by country and sometimes by state. Making sure it is lawful where you are, and that anyone entitled to be told has been told, is the responsibility of whoever operates the device.
Availability
CallVault is a private tool, distributed directly and not published on Google Play. It requires Android 11 or later and depends on Shizuku to capture call audio.
Download CallVault 0.2.9 · 86 MB · with its SHA-256 so you can check the file before installing it. · What's new in 0.2.9
Shizuku is not optional and there is no fallback. Android silences microphone access for apps in the background, so without Shizuku the app records nothing at all and says so rather than filing silence. Set Shizuku up first.
Setup & help covers installing Shizuku, sideloading the app, and how to confirm both sides of a call are actually being captured.