The rapid advancements in the field of materials science, especially nanoscience, have played a critical role in the advancement of sensors, in particular the development of novel transducer platforms. Sensors are devices that respond to specific phenomena with recordable and analytically useful output signals and have found their way into a myriad of applications in daily life. Some of these applications include the measurement of glucose and cholesterol levels and detection of emerging infectious diseases for biomedical purposes, environmental monitoring, and food analysis. 2D materials proffer numerous advantageous physical, chemical, electronic, and optical attributes such as large specific surface areas, excellent electrical and thermal conductivity, an abundance of catalytic sites, ease of functionalization, and tuneable electronic structures, allowing them to hold promising potential for the development of sensors with high sensitivity. Although layered materials demonstrate many beneficial attributes for the development of sensors, the properties and electronic structure of layered materials can be fine-tuned via doping or decorating to enhance the sensing performance. This review highlights the current progress of electrical and optical sensors based upon metal-decorated and metal-doped 2D materials and examines the effects of decorating and doping 2D materials for sensor developments.