Overwriting a Backbone Models Change Event

I think what I want to do is pretty simple I just don't know how to do it. I would like to fire my own event when one of my models attributes changes for the purpose of passing some data to the event handler (whether the change was an increase or decrease in value).

Basically I want my handler to do this in the view

handler: function(increased) {
   if(increased) {
      alert("the value increased")
   }
   else {
      alert("the value decreased")
   }
}

// ...

this.model.on("change:attr", this.handler, this);