Car Alarms: Pathfinder alarm wont turn off after replacing battery of truck, valet mode, nissan pathfinder

Question
QUESTION: I am the owner of a 2002 Nissan Pathfinder. It has been in storage for the last 3 years getting started and driven once a month.  My father in law replaced the battery in anticipation of my return and now he says that the car alarm won't quit going off. He tried replacing the battery of the clicker to no avail. If the battery is hooked up the alarm is going off.  Is there any quick fix for this?
ANSWER: Assuming this is an aftermarket alarm, you might have him try to leave the ignition on and reconnect the battery.  Some systems require this to prevent spikes from causing the alarm to trigger.  If this is a factory system simply pressing unlock on the remote would disarm it.  If trying the ignition on when reconnecting the battery does not stop the problem, take a look under the driver's side dash and try to find a pushbutton/flipswitch, this would be your valet switch.  Leaving the key in the run position and pressing this switch should also disarm the system if it is an aftermarket alarm.

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QUESTION: I bought the car when it was one year old. Is there a way to tell if the alarm is factory or after market? Also, if it is after market and the valet switch is necessary to reset it...does that permanently disarm the system and it will no longer be functional, or is this merely a reset button?  I am emailing all of your answers to my father in law for him to try out. Thanks in advance for all of your expertise!

Answer
A typical after market security system will have an LED indicator that flashes when the system is armed and illuminates solid when the alarm is in valet mode.  If your system does not have a LED then I would think it is the factory system.  However from the symptoms you describe it gives the 'feel' of an aftermarket.  If you have him take the dash panel(s) down under the steering column he should be able to see where the aftermarket system was tied into the factory system, following these wires back will expose the fuses that supply the system.  Removing these fuses will permanently disable the system.  If there were no wires tapped in and the system is a factory installed one and unlocking with the factory remote does not disarm the alarm I would suggest having a Nissan dealer take a look at it.