Answers to Frequently Asked Questions about Tella.
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Tella is a documentation app for Android. In challenging environments--with limited or no internet connectivity or in the face of repression--Tella makes it easier and safer to document events, whether that’s violence, human rights violations, corruption, or electoral fraud.

Tella has three main objectives:

  • Protecting users who engage in documentation from physical and digital repression.
  • Protecting the data they collect from censorship, tampering, interception, and destruction.
  • Empowering individuals and groups to easily, quickly, and effectively collect data and produce high quality documentation that can be used for research, advocacy, or transitional justice.

Tella is developed and maintained by Horizontal, a human rights non-profit organization. In addition to Tella, Horizontal develops other apps and tools and provides digital security trainings to activists, journalists, and human rights defenders.

Yes, Tella is free to download and use. It will remain free forever.

There are two ways to install Tella for Android:

  1. Get it here, directly from the Google Play Store.
  2. Install it manually on your device. You can download the APK (the file to install the app) from here.
Not yet, but we're working on it! Sign up here and we'll notify you as soon as Tella for iOS is ready.

Currently, Tella is available in:

  • English
  • French
  • Spanish

If you’d like to see Tella translated in another language, or if you’d like to help us translate, contact us here.

Tella's code is publicly accessible for anyone to review and audit here on our GitHub repositories. Rather than blindly trust us, audit the code yourself or ask someone you trust to do it. If you don't know someone who can audit our code, check out the report of the security audit conducted by Cure53, a security firm specialized in finding vulnerabilities. The report is available here on Cure53's website (note that at the audit was done on "Whistler", which Tella was initially based on).

Security & Privacy

Tella integrates various security measures in place to achieve an acceptable level of security:

  1. All data is encrypted at rest, on the user's device. This means that unless the app is unlocked (by entering the user's pattern), the data it contains cannot be accessed at all. Even if someone seizes the phone and extracts all the data using a computer, the data will remain unreadable. The encryption library we use is SQLCipher.

  2. All data being transferred between Tella and the servers we install for our partner organizations is encrypted through Transport Layer Security (TLS) and certified by Let's Encrypt.

By default, Tella only collects anonymized data for bug reports. Sharing bug reports can be disabled in the app in Settings > General > Share bug reports.

If you connect to a server and fill forms for an organization you work with, Tella shares the data that is attached to the forms. That data only goes to the organization's servers, never to ours.  

You can read Tella's full Privacy Policy here.

Yes, we're currently working on adding support for PIN and password! It will be released in early 2021. 

Tella includes a feature called “Verification Mode”. When Verification Mode is activated, Tella collects a whole bunch of information every time you take a photo, a video, or record audio. This information includes data about your device, your network, and your location. This information can then be used by researchers, lawyers, or journalists to verify the origin of the file.

For Verification Mode to be as useful as possible, Tella asks permission to access GPS location (specifically ACCESS_COARSE_LOCATION and ACCESS_FINE_LOCATION). You are free to deny this access, but the verification information will be less valuable to those attempting to verify the file.

Verification Mode is disabled by default, and Tella does not collect your location unless you activate Verification Mode.

You can read more about Verification Mode on this page.


When we talk about documentation, we mean any attempt to document things and events: this could mean taking photos and videos, recording audio and making interviews, filling forms and surveys, etc. 

Tella includes an "Offline Mode" for users who are collecting data in remote areas with limited or no internet connection. When Offline Mode is activated, all data is saved on the app and and users can submit it easily when they reach an internet connection.

All you have to do to collect data offline is:

  1. While connected to the internet, connect to your organization's server and download the forms you will want to fill.
  2. Enable "Offline Mode" on the app's homepage.
  3. Fill as many forms as you'd like and at the end of each form, where it usually says "SEND", tap "SAVE FORM". The forms will be marked as finalized and saved in Tella. 
  4. When you reach an internet connection, disable "Offline Mode", go to Collect > Sent, tap on the form that was saved, and tap "SEND".

Yes, we'd love to! Contact us here and tell us what you want to use Tella for and in what context you want to deploy it.

Tella is a project of Horizontal, a nonprofit organization serving frontline defenders, activists and journalists through digital security support and tool development.

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