Hyundai elantra 2002 alarm remote
 

Today i try to unlocking my car but it wouldn't unlock at all i put a new battery on my remote but it didn't work at all i when home got a my extra remote and it work my question is how do i know if a was my remote or something else?

Let me see if I understand the question:
One remote works perfectly fine and one remote doesn't work at all?
Hmmm.... What could be the problem?

Try swapping batteries in the 2 remotes. If the working one stops working and the other remote now works then the battery is the problem. If the same remote works and the other still doesn't work then the problem is the remote itself.