A flexible, body-mountable analyte sensing device includes a flexible substrate configured for mounting to skin of a living body. The sensing device additionally includes a sensor probe attached to the flexible substrate and configured to penetrate the skin such that a sensor disposed on the sensor probe can detect an analyte in interstitial fluid. The sensor probe can include an elongate extension of the flexible substrate. The sensor can be, for example, an electrochemical sensor or an optical sensor. The sensing device is configured to wirelessly indicate detected concentrations or other information about the analyte in the interstitial fluid. The flexible substrate of the sensing device is configured to be adhered or otherwise mounted to the skin in a manner that minimally impacts activities of the living body.