CTU3030 Finally- you select the appropriate level of noise for any given situation! Traffic light is computerized with adjustable sound level meter which can be set from 50 dB to 110 dB. Green light stays lit until noise in room goes above set level, then a flashing yellow light comes on as a warning. When sound level reaches 15 decibels above set level, a red light and siren sound come on (siren sound is optional). Lights can also be adjusted manually. Unit is 17" tall and can stand on its own or be mounted on the wall. AC powered.