HourGlass is a dual-function classroom management system that can be used as a Timer and as a Noise Detector. The giant display of lights is a dynamic measuring tool that can be seen by everyone in a classroom or even an auditorium. One year unconditional warranty. Requires 4 "C" batteries or optional AC adaptor (sold separately). Battery life in a typical classroom operation is 6 months- 2 years, but varies according to usage. Measures 15" x 8" x 4.5". TIMER MODE adds structure and focus to tests, games and other timed events. Everyone can see the lights fall from the upper part of the "sand timer" to the lower part. As "time's up" approaches the lights turn red, and a one-minute warning tone sounds. When the time is up, sound plays and lights flash to clearly signal the end. NOISE MODE helps control classroom noise. Everyone can see the rows of "sound meter" lights rise and fall, indicating the noise level in the room. At the "trigger point" set by the teacher, a warning sound plays and lights flash, signaling the room to quiet down!