Here’s how to lock down your Signal notifications. If you’re using Android: Open the Settings app, and under “Device” > “Sound & notification” select “When device is locked.”

The options are “Show all notification content,” “Hide sensitive notification content,” or “Don’t show notifications at all.” I recommend you choose “Hide sensitive information content” — this way you’ll still be notified when you get a Signal message (or any other sensitive notification), but you’ll have to unlock your phone to see who it’s from and what it says. If you’re using an iPhone: Open the Signal app and click the gear icon in the top-left to get to Signal’s settings. Under “Notifications” > “Background Notifications,” tap “Show.”

The options are “Sender name & message,” “Sender name only,” or “No name or message.” I recommend you choose “No name or message” — this way you’ll still be notified when you get a Signal message, but you’ll have to unlock your phone to see who it’s from and what it says.

To completely remove Signal notifications from your iPhone’s lock screen, open the Settings app, tap “Notifications,” scroll down to the list of apps, and tap Signal. From here you can turn off “Show on Lock Screen.”

You may also wish to poke through the settings for any other apps that display sensitive notifications on your lock screen and disable them.

Don’t Retain Your Messages Forever After your encrypted Signal message is sent to someone, copies of the plaintext message exist in only two locations: on your phone and on the recipient’s phone. (Unlike other messaging apps, the Signal server never has access to your plaintext messages, and only stores your encrypted messages on the internet for a short amount of time.) This means that if you delete the message from your phone, and the recipient deletes it from their phone, the message will no longer exist. It’s a good idea to regularly delete old messages, especially if they’re part of a sensitive conversation. This way, if your phone ever gets searched, the conversations you don’t even remember having from a year ago — as well as the sensitive conversations from last week — won’t get compromised. Signal lets you send messages that disappear from both your phone and the recipient’s phone after a specified amount of time (between 5 seconds and 1 week). This is useful when you and a friend both want to retain messages from your conversation for a short period of time. But keep in mind, nothing stops the recipient from recording the messages anyway before they disappear (like, by taking screenshots). If you have contacts or Signal groups (more on that below) that you regularly send private text messages to, I recommend setting disappearing messages to 1 week. It’s also easy to temporarily enable disappearing messages and then disable it when you’re done, for example when you need to send someone a password. If you’re using Android: Open the Signal app and tap on a conversation to open it.

Tap the menu icon in the top-right and select “Disappearing messages,” and choose the amount of time after the message has been seen before it disappears. If you’re using an iPhone: Open the Signal app and tap on a conversation to open it.

Tap the name of the person you’re talking to at the top of the screen to get to Conversation Settings.

Turn on “Disappearing Messages,” and choose the amount of time after the message has been seen before it disappears.

You can also manually delete individual messages, or whole conversations, from your own phone. Of course, this won’t delete them from the recipient’s phone — only disappearing messages will do that. If you’re using Android: To delete an individual message: Within a conversation, long-press on the message you’d like to delete to select it. Then tap the trash can icon at the top to delete it. You can also delete records of Signal calls within your conversation the same way.

To delete an entire conversation: From the list of Signal conversations, long-press on a contact to select it. Then tap the trash can icon at the top. This will delete all of the messages you’ve ever traded with that contact from your phone.

Enable “message trimming”: The Android version of Signal has a feature that lets you automatically delete messages in conversations that exceed a specific length. For example, you choose to retain the newest 200 messages with each contact, and automatically delete everything older than that. From the list of Signal conversations, tap the menu icon in the top-right and go to Settings. Tap “Chats and media,” and under “Message trimming” turn on “Delete old messages.” You can then adjust the conversation length limit, which defaults to 500 messages per conversation. If you’re using an iPhone: To delete an individual message: Within a conversation, long-press on the message you’d like to delete to select it. Then tap the “Delete” option to delete it. You can also delete records of Signal calls within your conversation the same way.

To delete an entire conversation: From the list of Signal conversations, swipe to the left on a contact and choose “Delete.” This will delete all of the messages you’ve ever traded with that contact from your phone.

To delete all messages in your Signal app: The iPhone version of Signal includes a nuclear option. To delete all of the messages you’ve ever sent or received, from the list of Signal conversations, tap the gear icon in the top-left to go to Settings. Tap “Privacy,” then “Clear History Logs.” Send and Receive Private Photos and Videos Signal makes it simple to send people encrypted photos and videos (including animated GIFs!). While you’re in a conversation with someone, just tap the paperclip icon to browse your photo library, or access your camera directly. But Signal also includes a subtle security feature: If you take photos or video with your camera from within the Signal app itself, these won’t automatically save to your phone’s library. Likewise, when you receive a Signal message containing a photo or video, this also won’t automatically save to your phone’s library. If you’d like to save a photo to your library, you can long-press the photo and choose to save it. Why does this matter? Many people automatically sync all of the photos and videos on their phones to iCloud, Google, or other cloud services. And people often allow other apps on their phone, such as Facebook or Instagram, to access their photo library as well. While convenient, this means that, after you’ve uploaded your photos to a cloud service provider, that provider can access them as well. And by extension, so can anyone who can convince the provider to hand over your data, like a law enforcement agency, or who hack your account, as in 2014, when nude photos of female celebrities were published online after their iCloud accounts were compromised. So, if you’re taking a photo of a top secret document to send to a journalist, or if you’re taking a sexy selfie to send to your bae, make sure to take these photos directly from within the Signal app — this way, they’ll have the same level of encryption and privacy as the rest of your Signal messages. Have Secure Group Discussions One of the most useful features of Signal, in my experience, is the ability to create encrypted group chats. Anyone can create a Signal group and add as many people as they’d like, and everyone in the group can send encrypted messages to everyone else. As with one-on-one Signal conversations, group chats support disappearing messages as well as photos and videos. Here are a few cases where Signal groups can prove useful: Communicating as a team on work projects that are too sensitive for non-encrypted tools like Slack or HipChat

Keeping track of your friends and colleagues at a conference

Keeping track of your affinity group at a protest

Organizing a weekly TV watching night

Running a rogue Twitter account as a team Here’s how to use Signal groups. If you’re using Android: From the list of Signal conversations, tap the menu icon in the top-right and choose “New group.”

Give your group a name, and pick which of your contacts you’d like to be a part of your group. Optionally, you can tap the circle to the left of the name field to choose an avatar for your group. Then tap the check in the top-right to create the group.

From within a group, you can click the people icon in the top-right to see a list of everyone else in the group.

From within a group, you can click the menu icon in the top-right for various options. You can click “Edit group” to change the group’s name or add new contacts. You can click “Leave group” to leave it yourself. You can also click “Mute notifications” if this is a noisy group and you don’t care to get notified for now. If you’re using an iPhone: From the list of Signal conversations, tap the pen icon in the top-right to start a new message. Then tap the people icon in the top-right to start a new group.

Give your group a name, and pick which of your contacts you’d like to be a part of your group. Optionally, you can tap the circle to the left of the name field to choose an avatar for your group. Then tap the plus in the top-right to create the group.

From within a group, you can tap the icon in the top-right corner for various options. From there, you can choose “Edit Group” to edit the group name or add new contacts to the group. You can choose “Leave Group” to leave the group yourself. And you can choose “List Group Members” to see who else is in the group with you. While Signal groups are useful, they’re not without problems. Hopefully these will improve in the future, but as of this writing: Anyone in the group can add new members, and it’s impossible to kick someone out of a group. People have to manually leave groups themselves. If someone who shouldn’t be in the group won’t leave it, you just have to make a new, separate group without them, and invite everyone else.

It can be annoying when someone in a group switches phones and their “safety numbers” change. (See more about safety numbers in the section below about verifying that the encryption isn’t under attack.)

There is a bug where, after you switch phones yourself, you’ll be able to receive incoming messages from groups you’re a part of, but you won’t be able to send messages to them yourself. There is a workaround: If another member edits the group, such as by changing its name, it will refresh the group settings and you’ll be able to post to it again. Make Secure Voice and Video Calls In addition to enabling secure text messaging, Signal can also be used to make encrypted voice and video calls. While you’re in a text conversation with someone, just tap the phone icon to call them. When they answer, you can just start talking to them like on a normal call, but with the assurance that the Signal call is end-to-end encrypted. If you’d like to start a video call, tap the video camera icon on your phone during a voice call to turn on your camera. That’s it. When you make a voice or video call, it’s possible for the person you’re calling to see what your IP address is, which could be used to learn your location. This probably doesn’t matter most of the time, but occasionally it might — for example, maybe you’d like to have a secure call with someone, but without letting them have any way of knowing what country you’re currently in. Signal has a feature that allows you to relay your calls through their server so that the person on the other end of the call can only see the Signal server’s IP address, and not yours. If you enable it, it will slow down your connection slightly, which might reduce the call quality. Here’s how to enable it: If you’re using Android: Open the Signal app, tap the menu icon in the top-right and choose “Settings.”

Go to Advanced, and turn on “Always relay calls.” If you’re on an iPhone: Open the Signal app and click the gear icon in the top-left to get to Signal’s settings.

Go to Privacy, and turn on “Always Relay Calls.” Most people sync their phone contacts to iCloud, Google, their employer, or other cloud services. This can be very convenient: If you lose your phone and buy a new one, you don’t lose all of your contacts. But this means that your contact list is accessible to the service providers you sync to — and by extension, it’s also accessible to law enforcement that can send data requests to those service providers. You might have some contacts that you need to talk to securely, but don’t want those phone numbers ending up in your contact list. For example, if you want to leak something to a journalist without becoming a suspect in a leak investigation, you’ll need to avoid having the journalist’s phone numbers in your contacts that get synced to the cloud. Signal allows you to start conversations with people that aren’t in your contact list. To do this, open the Signal app, tap the pen icon to start a new conversation, and type a phone number in the search field. If that phone number has a Signal account, you can then send an encrypted message — without adding the phone number as a contact in your phone. Verify That the Encryption Isn’t Under Attack Using Safety Numbers Sorry if this section is confusing for you — the inner-workings of encryption are always somewhat confusing. The important part is that you learn how to verify safety numbers below. I said earlier that Signal ensures your communications stay private when it is properly verified. Using Signal properly involves verifying that your communications are not subject to a “man-in-the-middle attack.” A man-in-the-middle attack is where two parties — Alice and Bob, for example — think they’re speaking directly to each other, but instead, Alice is speaking to an attacker, Bob is speaking to the same attacker, and the attacker is connecting the two, spying on everything along the way. In order to fully safeguard your communications, you have to take extra steps to verify that you’re encrypting directly to your friends and not to impostors. You and each of your Signal contacts share a unique “safety number.” For example, Alice has one safety number with Bob, but she has a different safety number with Charlie. When Alice compares the safety number she sees on her phone with the number Bob sees on his, if the numbers are the same, that means the encryption is secure. But if the numbers are different, something is wrong: Maybe Alice is seeing a safety number between her and an attacker, or Bob is seeing a safety number between him and an attacker, and this is why they don’t match. Because it’s unlikely that anyone is trying to attack your encryption the very first time you send a contact a message, Signal automatically trusts the first safety number that it sees for each contact. (If you discuss anything sensitive, you might want to confirm anyway). To verify that your encryption is secure, first navigate to the verification screen: Open the Signal app and tap on a conversation to open it.

Tap the contact’s name at the top of the screen.

Tap “Verify Safety Number.”