Capture Item Lookup Code before it goes on POS screen!

I'm doing little customization for RMS POS.

I need to get Item lookup code before it goes on POS transaction screen.

In other words when I type item number in POS screen and press enter, I need to intercept and get that number before RMS searches that item through inventory and adds to transaction entry.

If I use this mySession.Transaction.Entries.Element(I).Item.Description I get what I need but only after item is on transaction screen

Appreciate your response

Thanks,