Final answer:
The combination of a green reader light and a red tower light usually indicates a potential security event that must be evaluated by the security guard, who should follow specific facility protocols to handle the situation.
Step-by-step explanation:
If the reader light is green and the tower light is red, it typically signifies a condition that a security guard must assess and act upon according to the policies and procedures of the facility they're guarding. A green reader light usually means that a badge or access card has been accepted, while a red tower light might indicate an overall secured or alarmed state of the facility. The specific actions the security guard should take can vary, but could include confirming the individual attempting access has the authority to enter an alarmed area, checking surveillance for any breaches, or examining system status to ensure the alignment of security features.