To use the January app, you'll require a Continuous Glucose Monitor (CGM) to gather biometric data such as heart rate, activity level, and glucose levels. This data is essential for providing personalized insights and recommendations tailored to your unique physiology. The January app is compatible with devices like Fitbit, Oura ring, or Apple Watch. 

It's important to note that while using an activity tracker, like the mentioned devices, can enhance the accuracy of January's AI models and provide additional insights, it is not mandatory to use the January app.