A mobile device with a side-looking biometric sensor, a sensor and a method for sensing a biometric function of a user holding a mobile device a disclosed. In an embodiment, a mobile device has a generally flat rectangular shape with a relatively large front and rear surfaces and relatively small upper side, lower side, left side and right side surfaces, wherein the mobile device includes a sensor configured for capturing biometric data of a user holding the mobile device. The sensor includes a light source configured for emitting light towards a hand of the user and a photodetector configured for receiving light emitted from the light source and reflected back from the hand, wherein the sensor is a side-looking sensor.