Sidney Sarah Madge Czira (née Gifford; 3 August 1889 – 15 September 1974), known by her pen name John Brennan, was a journalist, broadcaster, writer and revolutionary. She was an active member of the revolutionary group Inghinidhe na hÉireann (Daughters of Ireland) and wrote articles for its newspaper, Bean na h-Éireann, and for Arthur Griffith's newspaper Sinn Féin.