Awareness of the dangers of overexposure to loud sound is increasing, but most people don't know how long they can listen to loud sound without risking hearing damage. Assessment of risk from noise exposure is complicated by the fact that many people are exposed to sound levels that vary considerably over time. Sound level meters are useful, but have limited predictive value because they measure sound only at one particular point in time. Noise dosimeters measure and integrate sound over many hours, and provide a more accurate measure of the noise dose experienced by the listener. Traditional noise dosimeters are costly and complicated. The ER-200 Personal Noise Dosimeter is inexpensive and easy-to-use: LEDs on the device display noise dose to alert users to the risk of over-exposure and the need for hearing protection. The ER-200D version includes PC-Interface software so data can be downloaded, saved and printed. This session will cover the basic concepts of noise dose, operation of the ER-200 consumer device and the ER-200D (data logging) device.