Abstract: Rarely software in the smart phone market can detect instantaneous heart rate quickly and precisely， because a threshold calculated based on a period of measurement is always necessary when using a derivative based algorithm. A phase demodulator based method was proposed to improve the performance of Android software. The pulse wave detected by cell phone camera was multiplied by a sine wave reference signal and then processed by a low pass filter to extract phase. The phase could be used to calculate the frequency beat to beat. Experimental results on an Android smart phone indicated that there was no obvious difference of instantaneous heart rate between the new method and the ECG method. Compared with derivative based and filter bank based algorithms， less phone resources was needed for the new algorithm and instantaneous heart rate could be obtained more quickly.

Key words: pulse wave detect；camera；Android smart phone, instantaneous heart rate, phase demodulator