The 3M(TM) Noise Indicator NI-100 provides users with easy, durable noise level detection, helping identify where hearing protection may need to be worn. users simply clip the Noise Indicator to a shirt or jacket; its LED light delivers a clear indication when noise levels exceed a potentially hazardous threshold. Red flashing LED: Noise levels are above 85 dBA - hearing protection may be required. Green Flashing LED: Noise levels are below 85 dBA - hearing protection may not be necessary. Please visit www.3M.com/NoiseIndicator for more details.