In its original form you would send a Tweet to the bot in a certain format and it would look up the specified gamertag and reply to the tweet with their current online or offline status.
My suggestion was that if the user is offline then it would continue to check the online status every minute and tweet when the gamer eventually came online. After a complete rebuild, and taking into account multiple requests for a single gamertag, having a 7 day limit to the checks and XboxAPI limit checks, it was complete.
Usage is really simple, just Tweet the following but be sure to replace 'Major Nelson' with any gamertag of your choosing. If it doesn't exist, you'll be notified by a Tweet.
@XboxAPI_Bot isonline Major Nelson