Biological indicators play a critical role in assessing soil functions and overall soil health, yet they remain underrepresented compared to chemical and physical indicators. Soil health is deeply influenced by the biological activity within, which is essential for nutrient cycling, organic matter decomposition, and overall ecosystem productivity. Extracellular enzymatic activities (EEA), in particular, provide valuable insights into how soil biological activity responds to external factors such as management practices, climatic changes, or pollutants. However, traditional methods for measuring EEA typically require complex laboratory setups, which limits their application in real-time field assessments. In this study, we introduce a novel, laboratory-independent soil enzyme activity reader (SEAR). SEAR utilizes an approach where soil enzymes react with fluorogenic substrates embedded in a transparent gel. Upon contact, the enzymes catalyze a reaction, producing fluorescent products that are detected on the opposite side of the gel. This enables a rapid and efficient assessment of multiple enzymatic activities, with the potential for analytical replicates and controls through the use of reaction plates with multiple gel compartments. We validated SEAR by spiking sand samples with varying concentrations of different enzymes, thereby establishing operational limits for rate detection, precision, and substrate concentration ranges. Our results demonstrate that SEAR performs reliably across a wide range of soil types, including sandy to silty clay loam soils, acid forest soils (pH < 4), carbonate-containing agricultural soils, and soils with up to 18% organic carbon content. Furthermore, the device was tested under various environmental conditions, including soil moistures ranging from 2% to 173% of water holding capacity and temperatures from 6°C to 50°C, successfully demonstrating its versatility for field applications. With SEAR, soil EEA measurements can be conducted quickly in the field, eliminating the need for laboratory access, sample storage, or pretreatment, which can alter results. The use of industrially manufactured reaction plates with strict specifications, combined with an automated data analysis pipeline, ensures standardized measurements without requiring specialized laboratory skills. In conclusion, SEAR represents a significant advancement in soil biological assessment by enabling fast, accurate, and field-ready measurements of EEA. Its potential for standardization and ease of use positions it as a powerful tool for soil scientists and environmental managers to assess soil health and functionality in real time across diverse landscapes and conditions. SEAR will also enable ongoing monitoring of soil biological activity, supporting long-term studies and adaptive management practices for sustainable land use. |