This paper presents an adaptive relay algorithm for Out-Of-Stability (OOS) detection that can be implemented in modern distance, line differential, and generator protection relays. The algorithm based Synchro-Phasor Measurement Units (SPMUs) for detecting the online system frequency used for calculating the online system angular speed. The algorithm is angular frequency-based for detecting the OOS condition for instant tripping and normal power swing that could be used for blocking the distance function from the abnormal tripping. Also, the algorithm is considered a remote breakers monitoring as it can detect fault clearing instant without any tele-communications between local and remote end substations. Single machine infinite bus (SMIB) test system is employed for validating the effectiveness of the proposed relay algorithm by making a comparative analysis between the Conventional Time Domain Method (CTDM) and the proposed relay algorithm.