[debugger] break on watch ?

I am looking in either the built in debugger or ptkdb.

Is there a way to set a 'floating' break point that will
stop the code execution when the value of a variable changes ?
Or when the value of a variable receives a certain value ?

Better yet when a hash changes ?

The point is that I don't know the code, I have know idea
where is this variable changed and there are lots of places in the code
where it can change.

thanks
   Gabor