Small wireless ultrasound device for continuously or semi-continuously signalling over a prolonged period of time a change in a body tissue, body vessel or body cavity, such as a bladder, comprising (i) at least one first electrical-acoustical element, such as a piezoelectric crystal or a MEMS, wherein the first electrical-acoustical element is capable of generating an ultrasound frequency pulse of 20 kHz-50 MHz, and at least one second electrical acoustical element, wherein the second electrical-acoustical element is capable of detecting a reflected ultrasound frequency pulse of 20 kHz-50 MHz, (ii) at least one processor for controlling the small wireless ultrasound device, (iii) an electrical power provider in electrical connection with the transducer and processor, (iv)a positioner for maintaining the small wireless ultrasound device in a position, (v) a voltage controller (d) for applying a voltage to the transducer, characterized by (vi) at least one sensor (b) for determining posture of a body of a user in a continuous or semi-continuous mode, such as a tilt sensor, and (vii) a direction means for directing the generating and/or detecting means, wherein the direction means is an array of transducers in a phased array, a set of transducers, mounted in different angles, where every transducer is used separately, or a mechanically movable transducer, and (viii) optionally a contacting means for contacting the small wireless ultrasound device to a skin of the body, and optionally an energy scavenger, wherein the at least one transducer is capable of operating separately, sequentially, in a phased array, in spatial scan mode, in intensity mode, in pulsed mode, or variations thereof, wherein the small wireless ultrasound device is wearable and is substantially flat, wherein the small wireless ultrasound device is adapted to configure itself automatically to an optimal signal and response setting, and wherein the wearable small wireless ultrasound device consists of one integrated package. (i) at least one first electrical-acoustical element, such as a piezoelectric crystal or a MEMS, wherein the first electrical-acoustical element is capable of generating an ultrasound frequency pulse of 20 kHz-50 MHz, and at least one second electrical acoustical element, wherein the second electrical-acoustical element is capable of detecting a reflected ultrasound frequency pulse of 20 kHz-50 MHz, (ii) at least one processor for controlling the small wireless ultrasound device, (iii) an electrical power provider in electrical connection with the transducer and processor, (iv)a positioner for maintaining the small wireless ultrasound device in a position, (v) a voltage controller (d) for applying a voltage to the transducer, characterized by (vi) at least one sensor (b) for determining posture of a body of a user in a continuous or semi-continuous mode, such as a tilt sensor, and (vii) a direction means for directing the generating and/or detecting means, wherein the direction means is an array of transducers in a phased array, a set of transducers, mounted in different angles, where every transducer is used separately, or a mechanically movable transducer, and (viii) optionally a contacting means for contacting the small wireless ultrasound device to a skin of the body, and optionally an energy scavenger, wherein the at least one transducer is capable of operating separately, sequentially, in a phased array, in spatial scan mode, in intensity mode, in pulsed mode, or variations thereof, wherein the small wireless ultrasound device is wearable and is substantially flat, wherein the small wireless ultrasound device is adapted to configure itself automatically to an optimal signal and response setting, and wherein the wearable small wireless ultrasound device consists of one integrated package.