[jQuery] Detect form change

[Gael]

Hi all !
I'm looking for a way to detect form change in jQuery. For exemple I
display a big and dynamic form pre-filled with values and splitted in
tabs.
I would like that when some form values in a tab is changed an icon
appears showing that a save is needed. I also would like to have an
alert if the user click on the menu without saving.
Is there an existing plugin or has someone already done this kind of
things ?
Thanks for your advices