In this study, we attempted to develop a wireless real-time continuous observation device for penile tumescence and/or stiffness for verification of nocturnal penile tumescence (NPT) and for diagnosis and classification of erectile dysfunction (ED). Unlike conventional mechanically wired method, the patient is not constrained by the device and is able to use the device by himself in his own living environment. A soft silicone ring that fits the penis is equipped with a built-in variable inductance, variable frequency oscillator and a one-time use micro-battery. The inductance (hence oscillating frequency) is responsible for the internal stress of the ring, which represents the tumescence and/or stiffness. A non-contact leakage flux coupled to the variable inductor allows proximity telemetry of the phenomenon overnight, or up to the battery life. Our prototype device was successfull in a feasibility test using a desktop model and in a simulated ex vivo test. Now, preparation for pre-clinical trial in healthy volunteer(s) is underway.