When you say unlocked it manually....Can you be more specific?
For example (I know from personal experience) if your window is down and for some reason the doors were locked, if you reach through the window and unlock the door and than open it the alarm will immediately sound.
Also, are you using the same key each time you unlock the doors?
If you could provide more details of what you are doing when it happens we might be able to help.
I assume when he means manually, he's using the key in the lock rather than the wireless remote.. I've done this before too and the alarm starts going off... I never tried this but in another car of mine you have to hold the key turned in the unlock position for a few seconds until it chirps.. good luck w/ it!
It is to prevent someone from picking the lock. If you lock the door with your key, not the remote, it will still sound the alarm. It assumes you are a lazy American (Or Canadian close to the border) and will never use the key. It is an idiotic feature, but protective one at that.
By placing your key in the car's ignition, bringing it to the starter and then putting it on ACC, it should stop its alarm (do not attempt to start it, it will lock the ignition I believe; and a call to OnStar will be in order).
Once in Canada, you can argue an entire point, defend yourself in court, and woo a lover just by the tone of "eh"
Such as, "Eh!" as you point at a man sitting in the defendant's chair would immediately bring him a guilty verdict.
Another action would be to look at a storm over head as your wife is stomping towards you to scold you for some thing you had done the previous night that she did not enjoy, and by saying "eh" a bolt of lightning turns her into Canadian Bacon (pun intended).