The treatment of low back pain usually includes exercise, analgesics, prostheses, and, in severe cases, surgery. Early treatments based on postural control are essential to prevent low back pain and mitigate permanent damage. This paper presents a wearable device with an estimated cost below $100 that uses inertial units with triaxial accelerometers, gyroscopes, and magnetometers to measure the orientation of three sections of the spine. The device integrates the absolute and relative orientations from the sensors to estimate the posture of the back in real-time and uses a fuzzy system to control a vibration unit that indicates to the user when to correct the posture of the back. This paper validated the device in controlled conditions, obtaining an rms deviation ≤1.24, and conducted a preliminary clinical pilot study with patients afflicted by lumbar hyperlordosis. This paper observed improved postural control and a reduction of low back pain in all cases. These results show the device's promising potential to reduce pain, improve postural therapies, and raise postural awareness in patients with low back pain.