I have a PhD degree in Electrical and Electronic Engineering from one of the most reputable universities in Turkey and have 15 years of microcontroller based systems design and 5 years of RF design experience.
Precise measurement of EMF levels require professional equipment of which cost is very high. Instead, in this project I will use RF detectors which are relatively cheap. This approach is suitable for personal use.
When measuring EMF levels, we need to specify a frequency range and a dynamic level range. Currently, we have a 300 MHz - 7 GHz detector capable of -32dBm to 10dBm readings available. This range is suitable for measuring EMF levels from devices such as laptops, PCs, mobile phones, tablets, monitors, etc. For measuring EMF from low frequency emitting devices such as hair dryers, other detectors are needed, which I can advise on.
Another point is antenna design. Although the RF detector is wideband, designing an antenna with that wide flat frequency response is not possible. So, some accuracy will be comprimised here. Also, EMF measurements are directional and necessitate taking the measurements on 3 (XYZ) axes. 3 antennas with 3 independent detectors are needed if the measurement is to be taken at once.
Although there will be comprimises limiting accuracy, a handy tool suitable for comparing EMF levels of different appliances can be designed.