A connector found on a motherboard that supports a chassis security feature that detects if a chassis component is removed or replaced, in which case an alarm sound is heard through the onboard speaker or PC chassis speaker if present. For the chassis intrusion circuit to work, the chassis power supply must be connected to AC power. By default, on the motherboard the pin labeled chassis “signal” and “ground” are shorted with a jumper cap. You need to remove the jumper caps if you intend to use the chassis intrusion detection hardware.
See also “Motherboards: What You Should Know” in the Quick Reference section of Webopedia.