2006 Kia Rio keyless fob

I have a 2006 Kia Rio that I have never had any problems with, but today I tried to use my keyless fob to unlock the door and it wouldn't work. I had to use the key to unlock the door. When I turned the ignition over the horn kept blowing. I turned the car off and tried it again and it worked. I shut the car off and got out and tried the fob again and it worked. What would have caused it to not work the first time.
Thanks