Newbie here and have a question.

I just recently purchased a 2000 S70. I had the check engine light come on and after running it with an OBD got the p1670 code. After reading on the forums found it, it is the Key Ring or Immobilizer. Purchased a new Key Ring and installed it. Only prob is when I went to start it the first, time the alarm sounds. Disconnected the battery for about 5 minutes and when I plugged it back in car started fine and check engine light cleared, boom back in business. But about an hour later I went to start the car and it started, but the horn sounded as well. Not like when the alarm is going off but just constantly on. Any ideas? When I bought the car it didn't come with the remote. Just the two keys, the master and the second key. Any advice would be greatly appreciated.

Thanks in advance.