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Tella features

All of the following features are available to all users as soon as they download Tella. They do not require any connection to a server or any special set up.

FeatureAndroidiOSAndroid FOSS
App LockPassword, PIN, PatternPassword, PINPassword, PIN, Pattern
Background encryption✔️✔️Not yet
Lock timeout configuration✔️✔️✔️
Camera silent mode✔️Not yet✔️
Screen Security✔️✔️✔️
Restrict unlocking attempts✔️✔️Not yet
Edit MediaCrop and Rotate PhotosCrop and Rotate PhotosNot yet
Encrypted file management✔️✔️✔️
Feedback✔️✔️Not yet
Import files from device✔️✔️Yes but missing delete original file
Preserve metadata when importing✔️✔️Not yet
Camouflage✔️Not possible in iOS✔️
Homescreen customization✔️✔️✔️
Camera (photos and videos)✔️✔️Yes but missing zoom, flip camera, enable flash and enable grid
Select video resolution✔️Not yetNot yet
Audio Recorder✔️✔️✔️
Open files in Tella✔️✔️Photos, videos, audio (not PDF)
Verification mode✔️Not yet✔️
Quick deleteFiles, Connections and TellaFiles and ConnectionsFiles, Connections and Tella
Quick exitLocks and closeLocksLocks and close
Connections to collect data and send files- Tella Web
- Uwazi
- Open Data Kit (Forms)
- Tella Web
- Uwazi
- Uwazi
- Open Data Kit (Forms)
Offline data collection✔️✔️✔️

App lock

When installing Tella, the user has to select a lock 🔒 to encrypt and decrypt the content of the app.

  • On Android, the user can select a pattern, PIN, or password.
  • On iOS, the user can select a PIN or password.

Without this lock, it is not possible to open Tella.


If the user loses their lock, it is not possible to regain access to Tella and the files stored inside the app. The user has to uninstall and reinstall Tella, and all files will be lost. 🔒🔑🚪

Video tutorial 🎥

Learn more about Tella Locks in our video tutorial

Background encryption

Tella encrypts files in the background so that users can continue performing actions (take more photos or videos, import more files, etc) while files are being encrypted. Users can see ongoing activities that are taking place in the background in a Background activity tray that's accessible from the Tella homescreen, by tapping on the "notifications" icon (🔔) on the top left.

While files are being encrypted, Tella displays an orange marker on the notifications icon. If the user opens the background activity tray while some files are being encrypted, they will see the list of files in the queue and the encryption progress.


If the user hard exit Tella (for example by using Quick Exit or minimizing the app) while files are being encrypted in the background, those will be lost.


If verification mode is turned on, then background encryption will be disabled, to make sure all file metadata is captured at the same time as the photo, video, or audio file is saved.

Lock timeout configuration

By default Tella will lock immediately every time the user exits the app or your phone’s screen turns off. If you’d like to change this setting, the user can do so by going to

Settings ⚙️ > Security > Lock Timeout.

The available options are 1 minute, 5 minutes, 30 minutes and 1 hour. ⏱️


Please use this feature carefully as if Tella is unlocked the data would be unprotected and anyone who enters Tella will be able to see all information there.


When the camera or the audio recorder are open, Tella won’t lock

Video tutorial 🎥

Learn more about Tella Additional Security Features in our video tutorial

Camera silent mode

By default Tella has camera silent mode disabled. By going to Settings ⚙️ > Security > Camera silent mode, it is possible to turn off the camera shutter sound to draw less attention when taking photos. 📷🔇

Video tutorial 🎥

Learn more about Tella Additional Security Features in our video tutorial

Screen security

By default Tella blocks screenshots, screen recordings inside Tella and hides the screen preview in the list of recent apps 📱🔒. It is possible to disable this security feature if the users need to take screenshots or screen recordings, or to mirror Tella to a computer for a presentation, by going to Settings ⚙️ > Security > Screen security.

On iOS screen security only blocks screen recordings inside Tella and blocks the screen in the list of recent apps, but it’s not possible to disable screenshots or screen recordings.

video tutorial 🎥

Learn more about Tella Additional Security Features in our video tutorial

Restrict unlocking attempts

By going to Settings ⚙️ > Security > Delete after Failed Unlock, the user can decide how many failed unlock attempts are allowed before everything inside Tella is deleted.

By default, this setting is Off, which means unlock attempts are not restricted and data won't be deleted. The user can choose to restrict unlocking attempts to 5, 10, or 20. If they choose any of these options, they can also select whether to display a visual indicator on the unlock screen 3 attempts before the specified number (3 attempts remaining, 2 attempts remaining, etc.), or to show no visual indicator at all.

After the specified number of failed attempts, all files, connections, and everything in Tella get deleted, and the user will go back to the "freshly installed" app state.


While this security setting prevents brute force unlocking attempts to enter Tella, it should be used with caution, as there is no way to restore the content of Tella once the maximum number of failed unlocking attempts is reached.

Edit Media

We are in the process of adding the ability to edit media files directly within Tella. Soon, users will no longer need to export their files outside Tella for editing. Tella Android and Tella iOS kick things off with photo editing capabilities (crop and rotate).

Users can edit a picture by going to More > Edit from the Images folder or by taping the Edit button on the top right while viewing image you have on Tella. On the Edit Image screen users can use the Rotate button on the bottom of the screen to rotate the image counter-clock wise or pinch and expand or contracts your fingers to move the white canvas to crop the picture. When edits are done, users can press the orange check on the top right of the edit screen.


All files stored inside Tella are encrypted. Without the app lock, it is impossible to decrypt and access any of the files stored in Tella. 🔒🔐

Upon installing the app, the user decides which lock method they would like to use. For Android, the user can use a six-point pattern, a PIN, or a password. For iOS, they can use a PIN or a password. The app cannot be opened without the lock.

Even if the device is plugged into a computer and all the device's data is extracted to be analyzed, all Tella content and data will look like gibberish and will be useless. Unlocking the app by entering the correct lock is the only way to decrypt, and therefore read, the content stored in Tella.


If the user’s lock is too weak, an adversary may be able to guess it and open the app on the phone; or the data could be extracted and a computer could brute-force the encryption key and decrypt the data.


If the user forgets their lock, there is no way of gaining access to the app and retrieving its content

video tutorial 🎥

Learn more about Locks and Encryption in our video tutorial


Technnical details about encryption can be found on the Security and Privacy section.

File management

Tella allows users to manage files and folders in a similar way they would do on a computer. All files and folders are encrypted and only accessible within Tella. 📂📝

In Tella, users can:

  • Store any file, including photos 📷, videos 🎥, audio files 🎧, and documents 📝.
  • Create folders and subfolders.
  • Move files into folders and from one folder to another.
  • Export files to their device. Once saved on their device outside of Tella, files are no longer encrypted and can be accessed by anyone searching the device.
  • Import files from their device. Files are automatically encrypted when imported into Tella.

Importing files from the device file system into Tella makes a copy of the files into Tella. Tella will ask if you want to keep or delete the original file from your phone when importing. If you choose to keep the original file, they will be present on the device, outside of Tella and unencrypted. 🔒


There are several options for Tella users to contact the Tella team in order to suggest improvements, report bugs and issues and request support. Inside Tella there are 2 alternatives:

  1. Email:

    • Navigate to Settings > About and Help > Contact us to find the email address.
    • Users can email the Tella team using their preferred email app.
  2. In-App Feedback Form:

    • Go to Settings > Feedback to enable an in-app feedback form.
    • This allows users to share feedback with the Tella team anonymously.

To ensure user privacy and anonymity, only essential data is transmitted to our Feedback server through HTTPS POST requests. Logs containing user information (IP address, date and time, and user-agent) are automatically deleted weekly.

On the Feedback server database, we only store a copy of the text sent by users in the feedback form and which platform it came from (Android or iOS).


The only information that we will receive is the content that users specifially add on the feedback form. If users are requesting support or want us to follow up with them, they should provide a secure way for us to contact them.

Import files from device

The user can import files into Tella to keep them secured by using the import feature. They can import files by going to the Add ( + ) button on either All files, Images, Video, Audio or Documents depending on the type of file they wish to import and then Import from device 📥. A prompt will appear asking the user if they would like to keep or delete the original file from their phone memory. The imported files will be kept secured at Tella.

video tutorial 🎥

Learn more about Collecting Evidence and Sharing data in our video tutorials.

Preserve metadata when importing

On Settings > Security users have the option to Preserve or delete the file's metadata when importing Photos and Videos to Tella. EXIF metadata of files migth include data about when the file was created, camera settings or location of the device.

Open files in Tella

Images, videos, PDFs and audios can be visualized inside Tella. 📱📄

On Tella FOSS, PDFs must be exported to be opened.


On Tella Android, it is possible to camouflage Tella in two ways:

  1. Users can change the name and icon of the app, to make it look like another app like a game or weather app. 🎮🌦️
  2. Users can hide Tella behind a fully functional calculator. In order to open Tella, the user must input their PIN into the calculator followed by = . The Calculator camouflage is only possible if the user uses a PIN lock. It is not possible to camouflage Tella as a Calculator if pattern or password is used. 🔢🔒

At this time, due to restrictions on the Apple App Store, Tella for iOS does not support the camouflaging features that are available on Tella Android.


The name "Tella" and its icon will remain visible in the Android settings. This means that camouflage will not protect against an individual actively looking for Tella on the phone or conducting an in-depth analysis of the device. 🔒👀

video tutorial 🎥

Learn more about Camouflaging Tella in our video tutorial.

Homescreen customization

By default Tella's home screen organizes files by type: 📷 images, 🎥 videos, 🎧 audio, 📄 documents, and other files. It also provides an All files section where all files can be accessed. For more information see File Management section.

For convenience and ease of access, it is also possible to customize the home screen to also show shortcuts to one or more of the following:

  • Recent files, to quickly open the newest files in Tella 💼
  • Favorite forms, for users connected to an ODK server 📝
  • Favorite templates, for users connected to an Uwazi server 📋

This configuration can be found in Settings > General.

Quick delete

A Quick Delete button allows users, in just a few seconds, to delete sensitive data within Tella. Quick delete can be configured on Settings > Security > Quick delete, where the user can choose to enable a sliding button on the home screen to quickly delete information from Tella in emergency situations. If enabled, the user can choose exactly what gets deleted when the feature is used. The available options are:

  • Delete vault: Deletes all files stored in Tella 🗑️
  • Delete draft and submitted forms: Deletes drafts and submitted forms in all Open Data Kit (ODK) connected servers 📝
  • Delete server settings: Deletes all server connections and all the forms or templates associated with them 📋
  • Delete Tella: Deletes the app and all the data it contains. It triggers a message asking if the user wants to uninstall Tella as well ❌.
Delete Tella

The Delete Tella option might not be available on some Android phones due to technical limitations. We are working on a fix for this issue. For iOS it is not possible to programmatically delete an app.

Quick exit

By clicking the exit button on Tella’s home screen right top corner, Android users can quickly close and lock the app in case of emergency. While having the lock timeout set to “immediately” means that the app already locks when the user exits, using the Quick Exit button adds an extra layer of security and assurance that the app will be fully closed and locked 🔒

On iOS, it is not possible to shut down an app from inside the app itself. Tapping the quick exit button instead locks the app.

Verification mode

In the Tella settings, users can activate "Verification Mode" ✅

When activated, every time a user takes a photo or a video, or records audio, Tella automatically captures verification information (file metadata). This verification information can be used to corroborate evidence, cross-check with other facts known about the event or about the area where it was captured. The verification information will be included as a separated file when saving the file to the device or when sharing it through third-party apps. The file format is .CSV with the metadata information included in columns. This file can be open with any spreadsheets app (like Excel, Google Spreadsheets, or OpenOffice).

Contact us

If you need help to better understand Verification Mode, feel free to contact us 😊

Below is a list of each piece of metadata captured by Tella:

Information about the file

  • File path: where the file was located in the Tella directory 📂
  • File hash: a unique number to identify the file 🔍
  • File modified: the date and time the file was last modified on the device 📅

Information about the device

  • Manufacturer: the name of the device manufacturer 📱
  • Hardware: the exact model of the device 💻
  • Device ID: a unique number identifying the Android device 🆔
  • Screen size: the exact screen size of the device 📏
  • Language: the language the device's operating system is set to 🌐
  • Locale: the geographic region the device is set to 🌍
  • Connection status: whether the device is connected or disconnected to the internet 📶
  • Network type: if the device is connected to the internet, specifies whether it is to a WiFi network or to a cellular network 📲
  • Wi-Fi MAC: a unique identifier to the device's Wi-Fi connector 🔍
  • IPv4: a unique address identifying the device's internet connection 🔗
  • IPv6: a more recent identifier to a device's internet connection 🔗

Information about the environment where the file was captured

  • Location: the exact location of the device, include latitude and longitude coordinates, altitude in meters, the accuracy of the measurement in meters, and the time 🌍
  • Location provider: how device location is determined 📍
  • Location speed: the speed at which the device is traveling 🚀
  • Cell info: the identifying numbers of all the cell towers the device is connected to 📡
  • WiFi info: the name of all WiFi networks in the vincinity of the device 🔍

Connecting to servers

Users can collect data directly in Tella, keep the data protected within the app, and connect to a server to securely send the data to a server. This feature is frequently used by organizations who centralize the data collected by volunteers or activist on the ground. These people collect information using Tella on their phones and then send it to their organizations. Previous Tella deployments where on-the-ground users collect data and send it to an organization's server have ranged from 1 to 2,000 users. 📲 📡

Currently the servers that can be connected to Tella are:

Video tutorial 🎥

Learn more about Connecting to Servers in our video tutorials.

Camera (photos and videos)

Tella offers a built-in camera where you can take photos and videos. All media collected inside Tella will not be available outside of it, as all files get encrypted as soon as they are taken. Files can only be accessed inside Tella, using the lock to open the app. Photos and videos won’t appear on the phone Gallery. In Tella, photos and videos will have a default name, but users can rename those using the Rename button. Files can also be organized in folders. 📷

The camera offers the possibility to change the resolution of videos before recording in order to save space: the lower the resolution, the less space the video takes, but also the lower the quality of the video. 🎥 💾

In Tella-FOSS, where we use the fully open-source CameraX library, some of the Camera’s features (zoom, flip camera, enable flash, enable grid, change video resolution) are missing.

Select video resolution

You can easily choose your desired video resolution on Tella by accessing the video recording screen and tapping on the Settings button. The available options include:

  • Highest possible resolution
  • High resolution (1080p)
  • Medium resolution (720p)
  • Low resolution (480p)

Video resolution refers to the number of pixels in each frame of the video. Higher resolutions, such as 1080p or 720p, result in sharper and more detailed videos. However, keep in mind that higher resolution videos also have larger file sizes, which may require more storage space on your device.

It's important to note that selecting video resolution is currently only supported on Android devices.

Audio Recorder

Tella has a built-in audio recorder. All audio recorded inside Tella will not be available outside of it, as all files get encrypted as soon as they are taken. Audio files can only be accessed inside Tella, using the lock to open the app. Recordings will not appear on the phone’s Voice Recording app or file system. In Tella, audio files will have a default name, but users can rename those using the Rename button. Audio recordings can also be organized in folders. 🎤 🎧

The audio recorder allows users to pause the recording and restart it as needed, keeping all the information on the same file. Users see how much space they have available while recording, to ensure they will not be out of space while recording. 📈 💾

Offline data collection

Once Tella is installed and configured on the phone, it doesn't need an internet connection to collect data. 📲 An internet connection is only needed to share files through other apps or through Connections. 🌐 If users have a server connected, once the forms or templates are downloaded to the phone, all data collected will be stored on the outbox tab and they can upload it to the server once they connect to the internet. 📩