Question: how to update one widget when another is saved/added?

Hi there,

Summary:
Is there a way to update widget A when widget B is modified/added/removed?

Details:
I’ve create an “alias” widget that outputs the content of any other active widget. In the admin, this widget has a drop-down <select> element that has an option for every other active widget. I would like the <select> menu to update when another widget is added/removed, and am not sure how to achieve this. In case this is unclear, here’s an example:

Save I have one alias widget and two other widgets: one text and one calendar. So the <select> in the alias widget shows:
– text-1
– calendar-1

Say I then drag a new pages widget into the sidebar. As soon as the widget is added, i would like the <select> in my alias widget to auto-update to the following:
– text-1
– calendar-1
– pages-1

Same goes for deleting the widget or moving it to an inactive sidebar – I would like the <select> to then auto update back to:
– text-1
– calendar-1

Is there a simple way to make this happen? Is it an ajax solution? Seems to me that I need to trigger the update function in my alias widget class whenever another widget is updated – does that sound right? If so, what filter/actions might I be looking for?

Thanks a ton, ya’ll – appreciate the help!
– Mickey