The Nissan Anti-theft System Is a very simple system but can be rather finicky. Specific sensory “conditions” must be present or the system will not arm and my not shut off if it does. To work the circuit must be grounded to sound the alarm when an entery way is opened. One of the common points of failure is the "Door Closed" switch. In it's location it is exposed to water and Winter salt which can corrode the contacts preventing it from alarming when the door is opened. This one in particular has a hole worn through the rubber boot exposing the switch to the elements. As you can see the switch plunger has poked through the hole.

This is the door switch. In it there are actually two separate sets of switch contacts. One for the dome light and one for the anti-theft system. The one furthest back from the plunger with the red wire is for the alarm. The other contact with the black wire and red stripe if for the dome light. Both share a common black ground wire. The type of switch contacts are called "Self scrubbing". This means that the contact surfaces scrape or "scrub" themselves clean each time they close preventing corrosion buildup. This also means they do gradually wear out. A well designed switch is a balancing act between excess wear and corrosion failure. However, with a hole in the boot, as in the above image, corrosion can build rapidly causing the dome light or the alarm to not activate.

The engine hood switch works much the same. When the hood is opened the switch closes and the alarm sounds. Replacing the hood during body work or making any adjustments to the fit of the hood and affect this switch. This switch can also fail if esposed to the elements. This switch must be “open” to arm the system.

The “Hatch Open” switch is a little more sophisticated. Unlike the other switches this one is incorporated directly into the latch assembly. Being in what is essentially the interior of the car this switch is less likely to fail due to corrosion. This switch must also be “open” to arm the system.