But now I can see why you want to detect the "enter keypress" - it's because your barcode reader appends it automatically at the end of the barcode string... so you'd like to detect it, eh?
I've actually worked with many Point Of Sale devices, when I was a device driver coder for a company selling POS-equipment and cash-register software. I had to create entire COM-interfaces for many devices according to the POS standard of the day.. The standard itself was rather beautiful and well designed, but no fun to implement. XD
Hopefully things in the POS arena have advanced a bit from those days, but maybe not.
Cheers,
AgentSam