Inclusion Criteria:  (a) Hong Kong resident, (b) Aged 18 or above, (c) Able to read and write Chinese, (d) Has regular access to a smart phone and internet, (e) insomnia severity index ⩾10; (f) Willing and can be contacted by experimenter via phone between 9 am - 9 pm  Exclusion Criteria:  (a) significant untreated/unstable mental or medical illness, (b) known factor to interfere with participation in this research, (c) serious medical, neurological, or psychiatric illness that may affect participation in this research, (d) sleep apnea, (e) concurrent treatment for insomnia, (f) unstablized medication that can affect sleep