Abstract: An anchoring or locking device to enable snap-in installation of boxes for electrical wiring devices in which the snap-in locking device is separate from the box and may be used universally with all types of boxes. The locking device includes a mounting base plate and means to attach the base plate to the side walls or to the top and bottom walls of an electrical wiring device box, the base plate having resilient fingers or extensions projecting therefrom at an incline starting from a point rearward of the box on which the device is mounted and extending at an acute angle from such point in a direction toward the front portion of the box. The projecting fingers or extensions are compressed inwardly toward the base plate when the box on which the locking device is mounted is pushed into the hole provided for the box in the wall on which it is to be mounted.