Apnea (involuntary stoppage of breathing for a while) is a very common phenomenon. While in adults apnea may just disturb the sleep, for neonates apnea can be life threatening. This paper describes a technique of detecting apnea using photo-plethysmo-graphy (PPG). The proposed technique is easily applicable for monitoring neonates on a long term basis for apnea detection since PPG is a non invasive technique that can be used for long term monitoring of patients, including neonates. In the proposed method, the respiratory signal that is inscribed in a typical PPG is extracted using wavelet decomposition. The onset of apnea is then detected by applying an algorithm on the power spectrum of the extracted respiratory signal. The apnea detection algorithm proffered was tested on 16 subjects and the maximum time taken for detection of onset of apnea is found to be less than 10 s (except for an outlier of 15 s), which is clinically acceptable. © 2013 IEEE.