Alert pop up after exploding block

[kzD1219]

Is it possible to have an alert pop up after a particular block is exploded?

I have a dynamic block, within that block there is a scale bar that needs to be changed to what scale the user is using.

Is there a way that every time after that particular block is exploded, an alert could pop up to remind to change the scale bar?? 

This is about all I know how to do...so not much:

(alert "Don't forget to update Scale Bar")

[Ranjit_Singh]

I believe reactors is the only way to do that.

[john.uhden]

I agree with @Ranjit_Singh that a reactor would be required to capture the explosion event and invoke an alert.  Might a user just erase the block?  If so, should he get a same or similar alert?  Might there be multiple insertions of the block, like maybe one per layout?  Might the explosion come from a Visual Lisp method rather than the "Explode" command?  But I guess the reaction code could be written to handle either event, maybe.