Kaiterra Sensedge Mini Installation Manual page 17

11. Attach the backplate onto the device
You will find three slots on the plate and three corresponding protrusions on
the back of the device. Line the device up with the plate such that the
protrusions are inside the corresponding slots. Rotate gently to secure the
device and lock it in place, and use the two fastening screws to fasten the
device to the plate.