Physical Layer Security (PHYSEC) has the potential to offer substantial advantages for key management for small resource-constrained devices. In this paper, we investigate two PHYSEC primitives: channel reciprocity based key generation (CRKG) and channel reciprocity based relay detection (CRRD). The security and entry performance of such systems in real-world scenarios are still open research questions. Until now, there are no embedded implementations of CRKG and CRRD systems providing resource requirements such as code size, number of clock cycles, and power consumption. Moreover, there are only few experimental verification of practical use cases that provide information about applicability and that cope with current security issues. We fill this gap with measurements carried out with our embedded prototype. By way of example, we address security critical remote keyless entry (RKE) use cases. To achieve this we created the first implementation of both PHYSEC primitives on an 8-bit SoC and provide practice-oriented performance results. Further, we provide a fair comparison to elliptic curve cryptography based key establishment schemes.