Alzheimer's disease (AD), which is characterized by gradual cognitive deterioration, is a serious worldwide health issue. Early AD identification is essential for prompt treatment and better patient outcomes. Digital biomarkers, which are products of many digital technologies, present a potential way to detect cognitive deterioration in AD early on. This article examines a variety of digital biomarkers and how they can be used to detect Alzheimer's disease, including cognitive assessment apps, eye tracking technology, voice analysis, keyboard interaction, wearables, neuroimaging, sensor-equipped homes, machine learning, biometric data, virtual reality, and social media analysis. Digital biomarkers have a lot of potential, but they also come with difficulties including validation, data protection, ethics, and regulatory issues. However, adopting these cutting-edge techniques offers the potential of earlier diagnosis, individualized therapy, and a better comprehension of Alzheimer's disease, marking a critical step towards improved AD management and, in the end, a cure.