Those db meters are cool but kind of expensive. This one is $249.
[link to www.action-electronics.com
Sound Level Meter with Alert with YOU'RE TOO LOUD!!! Alarm
Built-in YOU'RE TOO LOUD feature! Alerts users when sound level is too high.
Also records maximum level reached.
Optional accessories to switch on a light, give an alarm, alert some one that some one else is being TOO LOUD!!!
Bright LED's (red flashing or green) alert user when sound level is too high or too low - LED's can be read from 30m (100ft)
Continuous Monitoring of Sound Level 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.
Industrial, Hospitals, Classrooms, and special quiet zones When the sound level exceeds the HI set point the RED LED's flash and can be seen from 100 ft (30m).
Speakers/Educators/Instructors, Auditoriums and Theaters The user can set the SL130 so the RED LED's 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 LED's indicate the sound level is acceptable. The user can reverse the Red and Green LED's activation per user color preference.