In today's fast moving world, mobile phones have become one of the basic needs and mobile security is of a major concern. Mobile security is needed to assure a secured method for mobile transactions and to preserve data integrity and confidentiality. The present method of security involves password authentication. However this method is highly vulnerable to spoof attacks. Biometrics based authentication is a popular method of providing security. This paper proposes a novel method to provide security in mobile phones using biometrics. Among all the biometric modalities, Iris is proven to be one of the best traits and most suitable for authenticating mobile phone users. The challenging issue in the iris based authentication is localizing iris, the Region of Interest (ROI) and extracting features for real-time images due to varying illumination conditions. The proposed scheme adapts Sobel operator in color space and Contour method to accurately detect and segment the iris from eye image. The feature extraction is by Discrete Wavelet Transform (DWT), for accurate classification, simple k-Nearest Neighbor (k-NN) is taken and based on the percentage of match the authentication is done. The proposed algorithm is using JavaCV (Java + OpenCV), tested in Android 2.2 platform and implemented in Samsung I9003 Galaxy S with Android 2.2 OS, processing speed of 1 GHz and Internal Memory of 4GB. © Springer-Verlag Berlin Heidelberg 2012.