A great self-monitoring traffic light sound meter! This unique 17 1/8" traffic light is perfect for teachers to monitor noise levels in the classroom. The Yacker Tracker looks like a genuine stoplight and can stand on its own or be wall wall mounted; it is computerized with an adjustable sound level meter (effective from 40dB to 120dB). The teacher sets the sound level and the green light stays lit until noise in the room goes above the set level, then the green light goes off and the light flashes yellow. When the noise level reaches 20dB above the set level the red light and optional siren sound comes on. The user has the option of turning the siren sound off, which also makes this a great visual aid for hearing impaired students. The lights can be manually turned on making it great for debates and speeches. Includes: an AC Adapter and six replacement bulbs.