The VIBRA SE212 is a useful mid-range model with the wonderful added unique feature of vibration alert as well as audio visual alert for staying in your target heart zone. With digital coded transmit it it reduces signal interference and has several Smart Trainer Programs for monitoring exercise performance. Comes with all the usual features plus stop watch and Calculating Calories  & % Fat Burn. Can be used as wrist or wrist & chest-belt for optimum accuracy. Low battery indicator. The Dark Grey thicker SE212 is made for bigger wrists.