Start by swapping out the batteries. You can pick up new batteries for the fobs most anywhere (pharmacy, walmart, hardware store, etc.). Move onto inspecting for water intrusion if you have a sunroof. Check your fuse panel. Do other functions work on the remote fob? Are you able to lock/unlock with the buttons on the drivers or passenger side door?
Are other transmitters in the immediate area of where you're conducting testing? Can't "see" wireless signals, but you can see the outcome of interference. Try conducting the test in another area.
Sounds like you may need to get it checked out at the dealer though...