Cancer cases are rapidly increasing worldwide, with lung cancer being one of the leading causes of cancer-related deaths. Cancer detection at an early stage benefits in factors like better survival rate, faster prognosis, etc. There are various lung cancer biomarkers present in the saliva, feces, urine, and breath of human beings that can help in the prediction of cancer. One of the biomarkers is thyl Acetate present in human urine, whose detection leads to the early detection of lung cancer. For the sensing application, we investigated vacancy-ordered double perovskite, which is a high-potential material due to its optoelectronic and redox properties. In our work, we synthesised a vacancy-ordered lead free double perovskite using the chemical precipitation method and further explored it for sensing Ethyl Acetate (EA). Moreover, the material characteristics were investigated using XRD, UV, XPS, and Raman spectroscopy. Due to its low bandgap, the material efficiently absorbs visible light, enabling the generation of electrical power, thus enhancing its feature for self-powered sensors. Additionally, with ample vacancies, it shows excellent electrochemical sensing properties. It facilitated both electrochemical and photoelectrochemical EA sensing that was inspected in potentiometric and amperometric modes. The sensing material showed interesting results in both dark and light at -0.2 V. In the wide linear concentration range from 1 nM to 60 nM, the Limit of Detection is 3.55 pM. This sensor exhibits excellent selectivity towards interfering species, including urea, uric acid, glucose, sucrose, and ions such as Na⁺, K⁺, Cl^−, etc. The LSV approach demonstrates efficient real-time detection capabilities in simulated urine samples. Moreover, the self-powered sensor showed high selectivity, high sensitivity, low response, and low recovery time.