The battery life of a smart watch depends on the model. For example, Apple and Galaxy watches typically last about a day to a day and a half, but there are also models that can last longer. For the lesser known brands such as Colmi, Amazfit and Haylou, you can expect to get anything up to 7 days battery life.

Fitness trackers estimate calories burned by combining your body's motion with your height, weight, gender, and age. They also use a green LED light and light sensor to measure your heart rate through a process called photoplethysmography (PPG). However, this technology isn't always the most accurate way to measure heart rate.

Unlike other weighing scales that offer information only about your weight, Smart Scales are electronic devices that measure and track your fitness data, beyond weight. Of course, it measures your weight, simultaneously, it also calculates other health metrics like body fat percentage, metabolic age, bone density, etc.

Smart rings can track health and fitness, provide notifications, and enable contactless payments:

• Health tracking: Smart rings can monitor heart rate, body temperature, blood oxygen levels, and sleep patterns. 
• Fitness tracking: Smart rings can track steps, physical activity, and workout intensity. 
• Notifications: Some smart rings can vibrate or light up to notify users of incoming calls, texts, or other app alerts. 
• Contactless payments: Some smart rings have NFC (Near Field Communication) technology, which allows users to make contactless payments.

Smart rings are similar to smart watches in that they track activity, sleep, and well-being, but they don't have a screen. Smart rings also tend to have longer battery life and require less charging time than smart watches.