A "bug zapper" is a device that electrocutes bugs when they come into contact with its electrically charged inner panel. The bug zapper is typically mounted on a hook on the backyard porch so that the members of the house can sit outside and enjoy themselves without fear of being bitten. You can test whether a bug zapper is functioning correctly by observing a number of characteristics that are inherent in its operation. You will need a protective pair of glasses, but otherwise no special equipment.
Turn on the bug zapper. Place your ear a few inches away from its outer case. Listen for the distinct "humming" sound that indicates electricity is flowing through the now electrically-charged panel inside the case. Turn the bug zapper off and confirm that the sound is slowly diminishing to indicate that the once-charged grid is losing its electrical charge.
Turn the bug zapper on once it has become dark outside. Put on protective goggles to protect your eyes. Look at the color being generated by the electrified grid inside. A bluish color indicates that the zapper is working correctly and will electrocute any bug that enters it.
Stand next to the zapper and listen for the "hissing" and "cracking" sound that indicates a bug has entered and has been electrocuted. Stay nearby for an hour to confirm that the sounds are continuing as more bugs are entering and being electrocuted.