A wideband electromagnetic field (EMF) sensor system is introduced in this study. This small form factor, low-cost system is intended for use with smart mobile devices and can precisely measure the imminent field strength through the combination of a wideband omnidirectional receive antenna, RF, and audio mixing front-end as well as signal processing algorithm in the mobile unit. A detection dynamic range of 30 dB is shifted toward the high field intensity regimes to enable its use as a hazardous EM field detector. The total diameter of the device was 13 cm with a cylindrical thickness of 1.6 mm (standard FR4), and it can interface with the audio port of any mobile device including cell phones or tablets. Field strengths in the range of 5 V/m-50 V/m can be detected in approximately by 10 MHz-3 GHz RF transmission bands.