The Narda Nardalert is a personal RF monitor for electric fields with on site interchangeable sensor modules. The Narda Nardalert is worn on the body and gives visible, audible and vibratory warning when the electric field power density approaches or exceeds the permitted limit. The warning thresholds are user settable. Different sensor modules that can be exchanged on site are available for for various human safety standards. Sensor technology has been improved in this series by re-designing not only the sensor itself, but also by packaging it in a field replaceable package that contains all the electronic data necessary to maintain calibrated operation. This new feature allows your Nardalert to stay in service without costly logistics to keep multiple units calibrated - a major advantage for any NIR Safety Program. The Nardalert will always be capable of supporting new standards or guidance's and even different fields or frequencies, allowing future expandability and extending longevity.