Asus P2-P5N9300 User Manual page 42

9. Chassis intrusion connector (4-1 pin CHASSIS)
This connector is for a chassis-mounted intrusion detection sensor or switch.
Connect one end of the chassis intrusion sensor or switch cable to this
connector. The chassis intrusion sensor or switch sends a high-level signal to
this connector when a chassis component is removed or replaced. The signal
is then generated as a chassis intrusion event.
By default, the pin labeled "Chassis Signal" and "Ground" are shorted with
a jumper cap. Remove the jumper caps only when you intend to use the
chassis intrusion detection feature.
3-10 Chapter 3: Motherboard info