Telephone counseling at 1-week, 1-month, 3-month, 6-month, 9-month, 12-month and follow-up at 24-month are conducted with the participants to assess their smoking status (by questionnaire) and reinforce intervention (encourage quitting and providing quitting tips). Self-reported quitters who have quitted smoking for at least 7 days at 6-month are invited to perform saliva cotinine test (using NicAlert strip) plus exhaled carbon monoxide text to validate the smoking status.