Abstract: In an air purifier apparatus, an electrostatic filter is detachably and operatively connectable to an electrical contact which in turn is connected to a terminal of a power supply. The electrostatic filter is also detachably and operatively connectable to a second electrical contact which is connected to an alarm device. When the electrostatic filter is properly mounted within the air purifier apparatus, the two electrical contacts are short-circuited, thus electrically connecting the power supply to the alarm device through the electrostatic filter. The alarm device provides an indication that the electrostatic filter is properly mounted within the air purifier apparatus when energized by the power supply.

Abstract: A motor is connected in series with a power supply through a reversing device for reversing the direction of rotation of the motor and a speed control circuit. The reversing device includes two switches normally in a standby position in which the supply circuit of the motor is open. A command device is capable of alternatively and temporarily switching the switches into an operating position, for starting the motor in the respective opposite directions of rotation, when it receives a signal to do so from detector elements which generate the signal only when they detect a condition of normal operation of the control device of the motor.