Fast and accurate alarm of a seismic event is one of the most important tasks to reduce damage from earthquakes. This article proposes a new method for detection of P‐wave arrival that might be useful for a better earthquake early warning (EEW) system. As an existing method, short‐term average to long‐term average (STA/LTA) ratio is widely used to identify the onset time of earthquake using moving time windows. It calculates the averages of the absolute values of seismic wave in short and long windows and detects the outbreak of the seismic event when a ratio of them exceeds a predetermined thresholding value. The proposed method is based on the shape of moving empirical cumulative distribution function (MECDF) of absolute‐valued signal in a moving window. It requires one less window than the STA/LTA method, which alleviates the burden of optimizing window lengths while keeping similar performance. Furthermore, the MECDF method holds less parameter‐sensitive behavior in detection when the window length is not set correctly compared with the STA/LTA method. Hence, the proposed method is an alternative algorithm that facilitates the station‐wise parameter setting to detect P wave.