Inclusion Criteria:  Diagnosis of insomnia disorder Referral by general practitioner Aged 18 to 65 years old Insomnia Severity Index score over 14 Regularly uses a smart phone, which enable data synchronization with the MiBand2 activity wristband Able to complete self-administered study questionnaires Able to communicate in Cantonese  Exclusion Criteria:  Diagnosis of severe mental illness Personal Health Questionnaire 9 (measures depressive symptoms), score over 19 and/or anxiety symptoms (General Anxiety Disorder 7 score over 15); On regular pain medication during the last month, for more than 3 days per week Sleep affected by respiratory disease Regular user of alcohol or addictive substances.