A child safety seat includes a restraining device, and an alert device and a switch serially connected in a series circuit. The restraining device includes a strap and a tether connector provided at a free end of the strap, the restraining device having an idle position and a deployed position, the restraining device being arranged in the deployed position to engage with a corresponding structure provided in a vehicle for restraining the child safety seat. The switch is operatively coupled to the restraining device and has an open state and a closed state, each of the open state and the closed state of the switch uniquely corresponding to one of the idle position and the deployed position of the restraining device. The alert device is activable to emit an alert signal when the series circuit is closed.