To understand the behavior of the sensor noise we recorded for three hours at a fixed distance. We placed the sensor on a tripod to a distance of 1 m from the wall, using a sample frequency of 50 ms, then we recorded up to 200,000 data. In Fig. 4 we show a sample of the output for 100 s recording (upper panel) and the noise distribution (lower panel), where the mean value is 2.23 × 10−12 cm and the standard deviation is equal to 0.9 cm.