Signal is a private messaging application. Therefore, its functionalities are limited to preserve users' privacy. One of those options missing in Signal is the option to see the contacts' status, that is, to know if they are online or not, and the last time they were online. In short, it is not possible to know whether or not someone is online or offline in Signal.
However, the service does provide some information that may help you to answer this question. Thanks to read confirmations, you can indirectly find out if your friends are online. Signal messages can be found in four different states:
- Sending. The icon displayed next to the message is a circle with a dotted border. It means that the message is in the process of being sent. Or in other words, that it is coming out of your device.
- Sent. The icon displayed next to the message is a circle and a check symbol. It means that the message has been successfully sent to the recipient.
- Delivered. The icon displayed next to the message is two circles with check symbols inside. It means that the message has already been received by the recipient's device.
- Read. Displayed by two dark circles with verification symbols inside, it confirms that the receiver has read the message. This status is the best indication that the other user is online or at least has been online recently.
Although these icons are useful to know if another user is online or not, the fact is that they do not always appear. Why? Because Signal lets users disable read confirmations from the application's settings. In case your contact has deactivated them, you will only be able to know if your messages have been sent and delivered, but not if they have been read.