This paper describes CaptureMyEmotion, an app for smartphones and tablets which uses wireless sensors to capture physiological data together with facial expression recognition to provide a very personalized way to help autistic children identify and understand their emotions. Many apps are targeting autistic children and their carer, but none of the existing apps uses the full potential offered by mobile technology and sensors to overcome one of autistic children's main difficulty: the identification and expression of emotions. CaptureMyEmotion enables autistic children to capture photos, videos or sounds, and identify the emotion they felt while taking the picture. Simultaneously, a self-portrait of the child is taken, and the app measures the arousal and stress levels using wireless sensors. The app uses the self-portrait to provide a better estimate of the emotion felt by the child. The app has the potential to help autistic children understand their emotions and it gives the carer insight into the child's emotions and offers a means to discuss the child's feelings.