Extravasation is the leakage of intravenous fluids into surrounding tissues. It poses a significant risk, particularly in neonates, the elderly, and patients undergoing chemotherapy, with severe cases leading to tissue swelling and even necrosis. Conventional detection of extravasation relies on the subjective judgment of healthcare professionals, which lacks real-time capability and leads to a high miss diagnosis rate. While advanced monitoring methods like ultrasound, bioimpedance, and temperature sensing exist, they often require bulky equipment and incur high costs. Thin-film sensors offer portability and cost-effectiveness but typically rely on adhesives for skin attachment, limiting their reusability. To address these challenges, we propose a bioinspired adhesive coplanar capacitive sensor (BACCS) for accurate and timely extravasation monitoring. Inspired by clingfish suction discs, the patch features a discontinuous hexagonal pattern with central circular suckers, ensuring robust adhesion even under dragging. The resulting BACCS demonstrated strong adhesion to the skin, resisting displacement under tensile force, and accurately detected early extravasation in a mouse model. This technology holds promise for enhancing patient safety and treatment outcomes in intravenous therapy.