This read-only integer, ranging from 0 to 5, identifies which of the terminal's external input contacts triggered the accompanying wvExternalInputsStart or wvExternalInputsStop trap. An admin uses it to know which discrete external alarm input, often wired to a door sensor, generator alarm, or similar site equipment, changed state, since the terminal supports multiple such inputs. For example, wvExternalInputTrap reporting 4 alongside a wvExternalInputsStart trap tells the admin that input 4, perhaps wired to a shelter door switch, has just gone active.