When a cell of a workseet gets to a certain value excell creates a sound notification and creates an email
This really should be a feature. Smart-sheets has this. Its a shame that for all Excel's power/bells and whistles this is still missing.
Its really imperative if Excel online is to become a collaborative software.
Hope this gets taken seriously soon.
Corey Becker commented
You can do this with VBA I imagine. It's a pretty specific request for them to build a feature to do this. It would be interesting to have a simple user interface where you could set up alerts like this though.