Need a real time macro to prevent the duplicate entries between multiple worksheets

Hello Guys,

I need help regarding below concept:

There is a one excel shared file in which every user has his own worksheet to make application entries. All applications have unique application ids in column B. The concept says that only one entry has to be made for every unique application id regardless it has been entered in whichever sheet in workbook.

I need an help for creating a real time Macro (which runs in this shared file) which block users by givig an pop-up alert from making an entry of application ids which are already entered in the file. Through this we can hold the duplication of application ids.

Thanks,
Manish_Gupta