QardioCore turns itself on when you attach the chest strap to its left side and it turns off when you unclip the left side of the strap. When QardioCore is not being worn, if the strap is left attached to the device, QardioCore will remain in a low power mode to preserve battery life.
To check if your device is switching on, look for the short blink of a green light on the top of the device when connecting the chest strap to the left side of QardioCore. Always store QardioCore with the chest strap detached from the device.