So I get to work this morning, lock my car with the fob and all is normal. 5 minutes later or so I hear honking from outside, I think nothing of it, 5 minutes later it happens again and a coworker tells me its my car. Go outside, unlock it with the fob, all seems normal. Go to relock it with the fob and the security light on the dash starts blinking rapidly, which I'm assuming means the alarm is tripped. Unlock it, it stops. Do this a few more times with same result. All doors were closed and nothing was anywhere near the car.

Any ideas?

Do you have the shock sensor installled in your car ?.
If the answer is "Yes", it could be too sensative.
If the answer is "No", I do not have an answer for you that this time.

PS: When you lock your car using the fob, the security light will blink rapidly for 30 seconds, this is the stand by mode, then, it will slow down, two blinks every two seconds, indicating that the system is armed.

Nope no shock sensor.

Ah I didn't realize it blinked rapidly when first locked, I'll have to try again and see if it still goes off after a bit. Thanks.

Stupid question, but was the factory alarm an option? or was it standard on all 06 imprezas? I have opened my trunk and doors via the key and no alarm has gone off or anything.

To atleast try and be helpful though, I would check any and all sensor and door pin switches and their connections. A bad connection or a shot might trip an alarm.

Stupid question, but was the factory alarm an option? or was it standard on all 06 imprezas? I have opened my trunk and doors via the key and no alarm has gone off or anything.

The alarm is standard on all MY06 impreza models.
If the alarm has not gone off when you open doors and/or truck, verify if you are in valet mode.

I had the same thing happen. Were you sitting on your keys? If you hold down the lock button for two seconds it sets the alarm off. It went off in my garage and I nearly crapped my pants. I now take my keys out of my pockets when I lay down on the couch :-).