OBJECTIVE: Smoking during pregnancy poses significant health risks, necessitating accurate continuous monitoring of pregnant women's smoking behaviours. Existing methods relying on self-reporting lack objectivity, while biochemical measures like exhaled carbon monoxide (CO) provide validation but suffer from low participant engagement. We developed myCOtrak to address these limitations by integrating real-time CO monitoring with self-reported smoking, nicotine replacement therapy (NRT), and e-cigarette use. RESULTS: myCOtrak combines automated CO data from the Bedfont iCO monitor with daily surveys. It demonstrated high feasibility and usability in initial testing with 23 participants, with 75% continuing data submission for ≥ 14 days. Key features include seamless CO integration, cloud-based storage, and longitudinal tracking, offering a validated, scalable tool for smoking cessation research.