This paper proposes a new security technique for device authentication in Internet of Things (IoT) Wireless Sensor Networks (WSN). This technique, based on Polarization Shift Keying (PoSK), consists in using the polarization of the radio wave emitted by a device as a means of transmitting, in parallel with the main message, authentication data for this device or for the main message. Basically, this means cryptographically controlled modification of the polarization of the emitter outgoing wave. This is somehow a second modulation of the wave where the different used polarizations denote the symbols of this second modulation. Then, a security gateway synchronized with this emitter is able to retrieve these symbols. This creates a secure communication link between the two terminals at the physical layer. The PoSK mechanism should not alter the original waveform and its primary modulation enough to increase the bit error rate (BER). In this work, PoSK is experimented using two polarizations (Binary-PoSK), along with different primary modulations. The results show that this technique could be a way of achieving secure communications in IoT where devices are resource-constrained.