Authentication of Bluetooth devices on a per-packet basis is a challenging research problem since it is a low power technology with limited computational resources and storage capacity. In this paper, we describe a lightweight per-packet authentication protocol well suited for Bluetooth's constrained environment. The proposed authentication protocol is presented with one bit for authentication but could with facility be extended to $k$ bits for a higher security level. Since packets might be lost due to a bad wireless channel or an attack, the protocol needs to be robust and not lose synchronization of the authentication bits. A detailed description of a synchronization algorithm is presented and evaluated via simulation and analysis.