So you would like track more than just your weight? The One SmartDiet body composition analyzer can help. It can measure your BMI, body fat, water %, and BMR. The device is compact enough to fit in your pocket and also serves as an activity tracker.
The device is compatible with iOS and Android devices. It weighs only 0.7oz, so you can carry it around easily. The battery lasts for 168 hours. You can register multiple people for tracking.