Guys,
Ive got an issue with the alarm on my 02 4runner SR5 - I think it's the RS3200. My key fob has 3 buttons on the front. Lock, Unlock, and rear window down. On the back in the panic button.

Anyways, I went to unlock it today and the doors unlocked, but the horn started sounding as if the alarm was not disarmed. Oddly, inserting the key into the ignition switch started the vehicle and the alarm stopped sounding. I tried it again and the same result.

Any ideas what might be causing this?

Thanks for any help.