Searching Column A and puting a check mark in Column B

Hi,

I'm trying to make a simple function for my company for inventory purposes.
Basically I have the numbers 1-320 down column A. I want to be able to scan with my scanner a serial number (all which will be a number 1-320) and have it find the number I scanned in the list and put a check mark (or an X or something) next to it in column B. Any ideas?

Thanks,

Ryan Smith