The basic Alert setup would look like this:
which creates a scrolling text alert whenever a friend logs in - you can easily change the style of the response on the Response tab. The major points are the Channel and Pattern, I believe Standard is correct but as I didn't have any friends on to test with you might have to use the log feature to find the correct channel (just use "/alerter log show" to open the log and then start the log to see the channel and text of each chat message and have a friend log in to identify the correct channel and change the channel on the Trigger panel if I had it incorrect). The Pattern should be correct if I recall the message format correctly - if not, just use the logger to determine the pattern and replace the person's name with (.*) including the parenthesis. Note, the pattern shown is only for the EN client - for this to work for FR or DE clients you just have to use the log to capture the text and substitute for the name as show above and it will work fine.