Finding entropy sources is a major issue to design non-deterministic random generators for headless devices. Our goal is to evaluate a collection of sensors (e.g. thermometer, accelerometer, magnetometer) as potential sources of entropy. A challenge in the analysis of these sources is the estimation of min-entropy. We have followed the NIST recommendations to obtain pessimistic estimations from the dataset collected during our campaign of experiments. The most interesting sensors of our study are: the accelerometer, the magnetometer, the vibration sensor and the internal clock. Contrary to previous results, we observe far less entropy than it was expected before. Other sensors which measures phenomena with high inertia such as the temperature or air pressure provide very little entropy.