 When placed between the batteries and circuit board inside the front cover, tightening the screw base deforms and flattens the gasket forcing the battery tip to contact the back of the printed circuit board, which completes the circuit.Modern blinkees are more likely to use a battery case that opens with a small eyeglasses type screw and a push button on/off switch.The most common designs use a set of strong magnets, one at the back of the blinky, and another that can be removed.