"Touch heart rate readings depend on a strong, clear pulse to be read from your hands. In order to generate a clear signal, gently grasp the sensors. Do not tightly squeeze them, as this will negatively affect the pulse in your hands, making it more difficult for the sensors to get a good reading.
The sensors will be more successful if your hands are warm and moist. If you have difficulty getting a reading right away, try again after a few minutes of working out. Typically exercise will cause most people’s hands to become warm and moist.