Yacker Trackers appear to be mini traffic signals, but they actually indicate excessive noise in learning environments. The green light stays lit until noise in the room goes above the set level, then flashing yellow comes on as a warning. When sound levels reach 20 decibels above the set level, a red light comes on, along with an optional siren or “Quiet Please” warning — you can even record your own message. A 2-second delay prevents warnings when books drop or doors slam, and an LED counter tracks how many times units reach the red level. Stand-alone/wall-mountable units are powered by 2 AAA batteries or AC adapter (both included). Deluxe Yacker Tracker also includes a remote control with 20′ range.