Accelerometers are devices that measure acceleration and convert it to an electrical signal. The output is commonly in units of gravity (g). Most consist of some type of mass that accelerates and a sensor to measure its acceleration. They are mounted securely to the object being monitored in a way that limits damping of the acceleration signal. Accelerometers have been used in biomedical applications such as human motion analysis, motion detection vibration, and impact studies. As they are sensitive to acceleration caused by gravity, accelerometers can be used as tilt sensors, which measure the direction of an object relative to the ground. Applications of tilt sensors include sensing the onset of motion, biofeedback, and manipulation of handheld devices such as cell phones and wireless computer interfaces. Most accelerometers are based on semiconductor technology, and depending on device construction and properties, they can measure very small accelerations caused by vibration (micro g), or very large accelerations during motion or impact (thousands of g's). The performance capabilities of accelerometers have greatly improved over the past decade, due in part to advances in micro-electromechanical systems (MEMS) technology. As these devices become smaller in size, it is likely that more widespread use in biomedical applications will occur in the future.