A new, low-cost device that detects the presence of fog has been developed for applications including the active control of fog sampling equipment and the monitoring of fog spatial or temporal evolution. The new fog presence detector (FPD) offers an inexpensive alternative to visibility monitors and other specialized fog or cloud microphysical instruments that have typically been used for these purposes. The FPD makes use of a VCNL4200 proximity sensor (Vishay Intertechnology, Inc.) which operates as an infrared backscatter detector and was intended for proximity detection in cars, buildings, and personal electronics. An FPD with six individual sensors was evaluated in the field from 19 August 2019 through 4 November 2019. Over the course of the study, the FPD was able to successfully distinguish between foggy and clear conditions. The output from the individual sensors closely tracked one another and was strongly correlated with measurements of extinction coefficients from a collocated visibility monitor. However, the study revealed that a more powerful, external infrared emitting diode (IRED) was necessary for reliable fog detection when sunlight was present. With the inclusion of an external IRED, agreement between the FPD and visibility monitor averaged 91% when indicating the presence of fog during fog events. The FPD and visibility monitor were both found to be susceptible to insects and spider webs located in or near the optical sensing volume during foggy and non-foggy periods.