Facebook can make it very easy, or quite challenging, to see when a friend has come online. This capability depends on your friends' privacy settings and which devices they use for Facebook. The status icons in Facebook chat are usually the best indicators, since they can notify you the moment friends come online and when they last logged off. If your friend is hiding from chat or has disabled it, you can still often tell when she comes online by sending a message. Whichever method you use, it's important to understand that sometimes people appear to be online, even when they are not.
The easiest way to see if someone is logged into Facebook is to simply to look at the Facebook chat sidebar using any Web browser. Beside each friend's name is an icon indicating his online status. A green icon indicates you friend is online. A gray icon indicates your friend is offline, or wants to appear offline. If the sidebar is closed, you can open it by clicking the link in the bottom right corner of the screen. The sidebar usually lists friends you have recently chatted with, so if you don't see a friend in the list, you can type your friend's name in the search field at the bottom of the sidebar.
Understanding Chat Status Icons
The icons beside your name in the Facebook chat icon can vary depending on how you use Facebook. If you are online using a mobile app, a mobile phone icon appears beside your name. If you have Facebook messenger installed on a mobile device, or if you have the Facebook video calling plugin installed on your computer, a video camera icon appears beside your name. If you use a mobile app, the gray mobile app icon also tells your friends how long it has been since you were last online.
Hiding From Chat
It is possible to be on Facebook without being seen. There are two ways to be stealthy, both accessible from the gear icon at the bottom of the chat sidebar. If you turn off Facebook chat, you can appear offline to everyone. The advanced settings option also gives you the ability to appear online or offline to specific friends. If your friend has chosen to appear offline, you can send a message to that friend. As soon as your friend sees the message, Facebook will inform you by displaying "Message Seen" beneath your text.
No system is foolproof. Even when Facebook says someone is online or has seen your message, you can't assume this information is always accurate. If your friend has logged into Facebook and then walked away from the computer, Facebook will indicate that she is online and has seen your messages, even if she hasn't. The same is true for mobile apps. If Facebook is running in the background while your friend is on a phone call, it will appear that she is online and receiving your messages, even if she hasn't seen those messages. The only way to be absolutely certain someone is online using Facebook is when they actually respond to you.
Information in this article applies to Facebook as it appeared in April 2013. It may vary slightly or significantly with other versions.