With all respect: So should you.

Is the cell changing value because someone types something into it ? Or is
it because it contains a formula and some of its preceding cells are typed
into? Or is it connected to a database that changes something ? Or does it
query the internet ? Or is some macro changing the cell value ?

Is the dialog just saying something to the user ? Or is it asking for some
response, a choice of action or somethinbg ? Or does it perhaps require an
input of some sort, a typed value, a range, ... ?

Best wishes Harald

skrev i melding
ups.com...
Basically, something like:

If h17 0 then

msgbox("Message")

end if

But you should give us a deeper information about your wishes.