A system and method of monitoring sobriety using a hand-held breath testing device that, on receipt of a user's breath, generates a breath test signal comprising substance content data and user identification data, and wirelessly transmits the breath test signal to a breath test signal receiving station. The breath test signal includes substance content data and user identification data. The substance content data includes a blood alcohol level and the user identification data includes compressed image data. The signal receiving station is monitored by a supervisor who is able to intervene should the blood alcohol level be greater than a predetermined threshold, or should the user identification data no match with a reference user identification data.