I have a Holo Script model that uses the chatted even to spawn maps. Some custom chat systems completely remove Roblox's chat bar, leaving only GUIs. This means that the chatted event does not fire, even when a player chats using the custom system.
Is there anyway to get around this, or check if a place has a custom chat system?
I do not expect a code answer, just ideas from scripters on how this would be accomplished. Any answers are appreciated.

3 comments
You can try to create a bindable or remote event. This depends on if it's done in a local or server script. Then fire the event whenever someone chatted. http://wiki.roblox.com/index.php?title=API:Class/BindableEvent
It would be impossible in general to differentiate between a 'custom chat bar' and just any old TextBox -- or worse, a text label listening to keypress events.
What do you think about my idea on the comment of Immortal's answer?