Firewolf advanced photoelectric smoke detectors by Amityville, N.Y.-based NAPCO utilize two bicolored LEDs for indication status. In normal standby condition, the LEDs will flash green every 3 seconds. When the detector senses that its sensitivity has drifted outside the UL-Listed sensitivity window, the LEDs will flash red every 3 seconds. When the detector senses smoke and goes into alarm status, LEDs will latch on red.