Constructed with premium high-impact resistant thermoplastic materials and rational structure design, ensures superior strength and durability. Two Indicator Light provides simple, intuitive feedback on power and protection status. If the indicator (LED) glows green, you have installed the GFCI receptacle correctly and it is working properly. The GFCI outlet automatically conducts a Self-Test(the red light will blink once) every 40 seconds to ensure the GFCI is continually working. When the GFCI receptacle reaches the end of its' life the red indicator will turn on, it reminds you to replace the outlet in time. Tamper resistant(TR) -- TR design increases the electrical safety level by preventing the attempting to insert objects in to the outlet or open the plate. Provides continuous ground fault protection -- detects and trips on actual ground fault even when self-test is being conducted.