Nowadays’s authentication methods are essentially based on cryptography or any other kind of secret information. These methods are particularly efficient but they are, in certain cases, very power-hungry. As energy is a scarce resource in wireless sensor networks, we propose a new approach that consists in utilising the physical properties of the transmission medium in order to calculate, when receiving a frame, a confidence rating that we attribute to the source of the frame. This information is important in order to decide if it is necessary to authenticate the source using asymmetric cryptography. In the case where sensors are static and communications are slightly perturbed by the environment, the proposed rating can add another layer of control which enables sensors to check the origin of messages. This paper will also study how collaboration between the network’s nodes further enhances detection of malicious or third-party nodes.