The timely and rapid detection of pathogens and environmental contaminants is critical in safeguarding human health and preventing crises. Pathogens, antibiotic residues, pesticides, and heavy metals pose significant threats to human lives and the economy due to their rapid spread. Developing effective methods for detecting and preventing contaminant spread remains a major challenge. Researchers have been exploring innovative sensing approaches to enable easy, portable, and cost-effective detection using smartphones as versatile sensing tools in recent years. Integrating smartphones with detection assays allows for convenient result acquisition through a simple photograph. Aptamers, with their high affinity and selectivity, have gained substantial interest in biosensing, and they are increasingly employed in the design of novel detection assays based on optical or electrochemical principles. Additionally, smartphone applications can be developed to process images and analyze results based on optical or electrochemical signals, accurately determining pathogen loads. Apart from aptamers, smartphone-based detection platforms also utilize other sensing elements, such as antibodies, carbohydrates, and proteins. Coupling smartphones with detection assays simplifies the detection procedure, making it portable and highly sensitive. This review focuses on the latest technological advancements in smartphone-based devices for biosensing applications, highlighting their potential for rapid pathogen and contaminant detection.