What are all the events that cause a Game Beacon to notify you/other players?

When you set up a beacon you can initially choose to just share it with your xbox live friends but also on facebook. After sharing, your friends will be able to see your beacon in different ways. One of them is when they launch the game you want to play, then they will get a notification saying "Gamertag wants to play this game". The other way is for them to go to the beacons section where they can see a list of all their friends' beacons. You will get a notification everytime one of your friends launches a game that you have set up a beacon for as well so you can contact them.