From the owners manual.
The alarm will be activated if any of the following occurs while the
car is parked and the system is armed.
- A front or rear door is opened without using the transmitter or the ignition key.
- The trunk lid or tail gate is opened without using the transmitter or the ignition key.
- The hood is opened.
The siren will sound and the turn signal lights will blink
continuously for about 30 seconds (This will repeat 3 times). To turn
off the system, unlock the door or trunk lid/tail gate using the
transmitter or the ignition key.
The system will be disarmed by using the transmitter or the ignition
Now the way that reads it seems that opening the door with the ignition key won't make the alarm go off. In my experience it means if you use the ignition key to turn on the ignition it will disarm the alarm. Most cars I am familiar with will do some type of pre-warning when the door is unlocked using the key, and if the ignition key is used to start the vehicle within x number of seconds the alarm will not go off. Even if it goes off in your case try starting the car and that may silence the alarm.
As far as battery replacement the owners manual also addresses that.
Replacing the battery
When the transmitter's battery becomes, it may take several pushes on
the button to lock or unlock the doors, and the LED will not light.
Replace the battery as soon as possible.
Battery type : CR2032
Carefully separate the case with a blade screwdriver as shown in the illustration.
Remove the old battery from the case and note the polarity. Make sure the polarity of the new battery is the same (+side facing down),
then insert it in the transmitter
Also note unlike the Audi you will NOT have to reprogram your remote.