Measuing your heart rate using an optical sensor on the underside of the watch, Garmin Forerunner 235 allows you to run without a chest strap. A built-in accelerometer captures distance and pace data when you\'re running on an indoor track or treadmill. The colourful gauge detects your heart rate zone and live beats per minute. Once you\'re done running, it doubles as an activity tracker, counting your steps and calories throughout the day.Using bluetooth, hook up your compatible smart phone to recieve notifications and with an impressive battery life, it will last longer than its predacessor, the 225. Its comfortable and smart for daily use and wear and will be the only running watch you\'ll ever need.Features Bluetooth Smart wireless sync Optical Wrist HRM Activity Tracking Graphical Interface VO2 Max Estimates Longer Battery Life Smart Phone Notifications 5 ATM water rating Display Size: 1.23inch / 31.1mm Dimensions: 4.6 cm x 4.6 cm x 1.3 cm Weight: 42g