Horn blasting, lights on- wtf??

So my wife went to start our 2002 Silv. tonight and when she turned the key, instead of a purring truck we got a blasting horn. We had to pull the relay to get it to quit. The cab lights are all on, and the door alarm is dinging even though the keys are not in the ignition. The truck does not attempt to start in any way when the key is turned, and the security light is blinking.

What the heck is up? We pulled the battery cable off to get the thing to quiet down. Upon hooking it back up, it immediately goes back into its temper tantrum.

Help!

How long did you leave the cable unhooked? I assume that you unhooked it again to silence it, have you tried hooking it up again since? Sounds like the computer that controls all the security stuff is messed up. Has to be left unhooked for at least a few minutes to truly reset it, I believe.

Do you have an alarm? Did she maybe hit the panic button by mistake?

The craziness with reconnecting/disconnecting the battery isn't uncommon. If you have an alarm, even if it's turned off it'll go nuts until it's disconnected/connected.

make sure you have a good connection to the battery and that everything is dry and have no shorts i