During a Code Red drill on a medical-surgical unit, the nursing staff is instructed to implement the emergency response plan. One of the critical responsibilities of the staff is to identify and secure exits to ensure patient safety. In preparation for any emergency, all nursing staff must be prepared to respond according to the facility's guidelines. Given this situation, fill in the blank: In the event of a fire, the first action that should be taken according to the emergency response plan is to immediately activate the __________ system.