Install a 3/8-inch diameter glass cutting bit into a power drill or a hand-held oscillating tool.
Fill a spray bottle full of cold water and screw the top on tightly. Put on safety glasses and work gloves before proceeding with drilling through the glass.
Walk to the exterior of the home so you are facing the double-paned window. If the window is above ground level, use a sturdy ladder to access it easily.
Place the tip of the drill bit in the lower right corner of the glass and squeeze the trigger to begin drilling through it. As you drill, spray the bit constantly with water from the spray bottle to cool it off. If is helpful to have another person perform the spraying.
Continue holding the bit in place until it penetrates through the exterior pane of glass. Do not drill all the way through the interior side of the glass.
Reposition the bit at the upper right corner of the double-paned glass window and repeat the process to drill a hole in this location as well.
Wipe down the external surface of the window with a cloth to remove the excess moisture.