distance between bollinger bands

 
I am looking for an indicator which gives the distance between bollinger bands and can detect the rate of change of the distance between Bollinger bands, and that alerts can be set on the values. Any body know of 1?
 

Through the documentation listed by qjol you will be able to find that the price of the high and low bands for any given bar. I'd say it's pretty good project to start learning MQL4.