A tank-in-tank fill level indicator, making use of noninvasive tank-in-tank measuring techniques. A vibration device, such as an exciter or resonator, vibrates the outer tank at its natural frequency of vibration, thereby inducing the vibration of the inner tank and a beating effect as a result of the interaction of the vibrations of the two tanks. A vibration detection device, such as an accelerometer, detects the resultant beating effect of the two tanks' induced vibrations. A data processing device, such as a microcontroller, processes the detection data to obtain the liquid volume. A display, wired or wireless data transmission device, or combination thereof, is then used to provide tank or container fill-level information.