A Project of the Electronic Frontier Foundation 
Signal is a free and open source software application for Android that employs end-to-end encryption
, allowing users to send end-to-end encrypted group, text, picture, and video messages, and have encrypted phone conversations between Signal users on both iPhone and Android. Although Signal uses telephone numbers as contacts, calls and messages actually use your data connection; therefore both parties to the conversation must have Internet access on their mobile devices. Due to this, Signal users don’t incur SMS and MMS fees.
Installing Signal on your Android phone
Step 1: Download and Install Signal
On your Android device, enter the Google Play store and search for “Signal.” Select the app Signal by Open Whisper Systems.
After you click “Install,” you’ll see a list of Android functions that Signal needs to be able to access in order to function. Click “Accept.”
After Signal has finished downloading, click “Open” to launch the app.
Step 2: Register and Verify your Phone Number
You will see a screen that looks like this:
Enter your mobile phone number and click “Register.” In order to verify your phone number, you will be sent an SMS text with a six-digit code. Since Signal can access your SMS text messages, it will automatically recognize when you’ve received the code and complete your registration.
Using Signal
In order to use Signal, the person that you are calling must have Signal for Android or iOS installed. If you try to send a message to someone using the Signal app and they do not have Signal installed, it will send a standard, non-encrypted text message. If you try to call the person, it will place a standard phone call.
Signal provides you with a list of other Signal users in your contacts. To do this, data representing the phone numbers in your contact list is uploaded to the Signal servers, although this data is deleted almost immediately.
To get started, click the pencil icon in the lower-right corner of the screen.
You will see a list of all the registered Signal users in your contacts. You can also enter the phone number of a Signal user who isn’t in your contacts. When you select a contact, you’ll have the choice to either call them or send them a message.
How to Initiate an Encrypted Call
To initiate an encrypted call to a contact, select that contact and then click on the phone icon. You’ll know that the contact can accept Signal calls if you see a small padlock icon next to the phone icon.
Once a call is established, both parties to the call will be shown a random pair of words. This word pair will allow you to verify your identity and keys with the other user—also known as key verification.
The most trustworthy way to verify the identity of a caller is to use out-of-band verification to verify the word pair. You can also read the words aloud if you recognize the caller’s voice, although very sophisticated attackers might be able to defeat this if they needed to. The word pair must be identical on both users' phones for you to be sure your message is not being intercepted.
How to Send an Encrypted Message
In order to send an end-to-end encrypted text, picture, or video message, navigate to your contact list, click on the contact’s name, and send your message.
You can send an encrypted group message by clicking the overflow icon (the three dots in the upper-right corner of the screen) and selecting “New group.”
Using this app can help to keep your communications safer since everything sent via Signal is always end-to-end encrypted.
Note that Open Whisper Systems, the makers of Signal, use other companies' infrastructure to send its users alerts when they receive a new message. It uses Google on Android, and Apple on iPhone. That means information about who is receiving messages and when they were received may leak to these companies.