Short for Permissive Action Link. PAL is an ArmsTech-designed security system used as a safety device to regulate the release and launch of the nuclear warheads at the nuclear disposal site on Shadow Moses Island. Two detonation codes must be entered to enable control of the nukes. The two hostages on Shadow Moses - DARPA chief Donald Anderson and ArmsTech president Kenneth Baker - each knew one. In case of emergency, PAL is also prepared with a special key that enables emergency release and detonation of the nukes without inputting the codes. When Solid Snake infiltrated the nuke building on Shadow Moses, he received this key from Meryl through Kenneth Baker. The system requires three types of keys, but there is only one actual key. The key is made of a shape-memory alloy that changes shape depending on the ambient temperature, essentially functioning as three keys in one.