The disclosure describes a sensing device that is implantable to sense bladder conditions, as well as a neurostimulation system and method that make use of such a sensor for alleviation of urinary incontinence. The sensing device is implantable outside the bladder, but includes a lead that penetrates the bladder wall to deployed a sensor within the bladder. Using the sensor on the lead, the sensing device outside the bladder is able to detect a condition within the interior of the bladder. In this sense, the sensing device provides transmembrane sensing of internal bladder conditions. The condition may be indicative of bladder filling or bladder contraction, and may be used to control electrical stimulation applied to the patient to alleviate urinary incontinence.