The Extech SL130W-NIST Sound Level Alert with Alarm, 30-130dB Meter with built-in LEDs indicators, is a sound level alert with alarm for continuous monitoring of sound levels. Ideal for industrial, hospital, auditoriums, schools and other areas where there is a need for being alerted when sound level reaches set points. Bright LEDs (red flashing or green) alert user when sound level is too high or too low - LEDs can be read from 30m (100ft). You can set the SL130 so the RED LEDs flash when the sound level is below the "LO" set point where people in the audience may not be able to hear. When the sound level is above the "LO" set point, the GREEN LEDs indicate the sound level is acceptable. You can reverse the Red and Green LEDs activation per user color preference. Wall, desk or tripod mount with optional 15ft (5m) microphone extension cable for remote monitoring. User settable high or low limit (30 to 130dB) with output to drive external relay module. Meets ANSI Type 2 and EN 60651 accuracy specs - compliant to OSHA. 8 x AA batteries (not included) can be used for monitoring function only without LED alert. It includes NIST Certification.