I use PSI, an open source desktop chat client to connect to a jabber server I run at work, and also to connect to Google Talk (aka Google Chat, Google Messenger, Google Hangouts - whatever they are calling this XMPP based instant messenging service this week). I've used this setup for years, PSI accepts connection to my PGP key so I can chat over encryption for conversations I wish to remain private (sending passwords or discussing finance, etc.) and still have the rest of my chats stored in gmail for searching as needed. This way I don't need to keep a browser window open and be logged into gmail all the time just to stay connected for chat.

In PSI you can hover your mouse over a contact and some interesting info will be displayed in a little pop-up window including the user's avatar (image), username, last status on system (when they were last connected) and a Resource ID which represents the machine on which they are running their chat client. There may be more than one resource shown if they are logged into a particular account from more than one device. These days thats fairly common as many folks have a laptop (which they leave on and just close the lid) as well as a smartphone and both are logged into a chat client like Google messaging. The client type can be guessed by analyzing the resources listed. It has been observed that:

Android device starts with "MessagingA"
iOS device starts with "MessagingB"
Google+ chat: starts with "messaging-TalkGadget"
Old chat in Gmail: starts with "gmail"
New hangouts chat in Gmail: starts with "messaging-smgmail

I am aware of the various devices I own, and when they are on and I am logged into my Google account, so I was surprised recently when I happened to notice that there were several lines of resources listed for my connection which did not seem to correspond to any of the devices I was using. Valid resources were shown which were easily identified because I like to set the client to display the machine name instead of a random text identifier, but there were also several resources that all began with MessagingA. This indicated they were from Android devices, and I have a couple of them, but when I logged in with these devices I would see them appear as expected in addition to these mysterious resources.

This was initially a cause for concern, and I thought at first that perhaps someone had gained access to my account and was "camping on" to my chat stream from some android device somewhere. As it turns out, thanks to some investigation done by a friend at work it appears more likely to be related to some messing around I did recently flashing Cyanogenmod on my Samsung S3. According to this thread, if you close or delete a Google Messaging app without signing out of it first you can leave "orphaned" connections like this which are eventually removed after 1 month. I haven't found any way to remove this orphaned connections manually.