Bluetooth low energy beacons have gained traction among ambient intelligence researchers. Their low cost and robustness make them a fit choice for ambient assisted living or other healthcare applications. Nevertheless, similar to many other radio-frequency based technologies, beacons pose serious challenges when it comes to developing applications that require predictability. Moreover, the multipath propagation characteristics of Bluetooth beacons prevent ambient intelligent researchers to solely rely on using theoretical models to describe their behaviors. In this paper, we present an empirical evaluation of Bluetooth beacons behaviors. We describe the observed pattern of the signal through a series of experiments totalizing more than 3 million samples.