The Yacker Tracker appears to be a traffic signal, but actually signals too much noise. Just select the appropriate level of noise for any given situation and let the Yacker Tracker be a visual and audio reminder when the noise level gets too high! Aim: To provide a visual signal of too much noise for children and students of all age levels. 17"h x 5 1/2"w x 5"d. Sold as Single Unit. You can set the level with which you are comfortable. Visual signal of when it is too loud. Great for classrooms, cafeterias and much more. Works with students of all ages.