For IFR GPS approach certification, GPS status annunciations are required to be in the pilot's field of view. These annunciations (or lights) indicate active switches such as the NAV/GPS and OBS (if applicable) modes. Other annunciations or alerts might include the following:
TERM - light that will signal pilot when operating within 30 miles of departure or arrival airport (i.e. Terminal area)
APR - light that signals pilot when the GPS is engaged in Approach mode
MSG - light that signals pilot that the GPS has generated a Message alert that should be viewed on the GPS
WPT - light that signals pilot that the GPS has generated a Waypoint alert that should be viewed on the GPS
INTG - light that will signal pilot when the GPS receiver detects a position error or is unable to calculate the Integrity of the position
Some annunciator units and annunciator control units or ACUs have a variety a these switches and annunciators depending on the GPS system to be interfaced with or the aircraft installation. However, there are certain annunciations such as MSG and WPT that are standard for all annunciators required.