A rat zapper is a trap that lures in rodents and disposes of them through electrocution. It uses two metal plates or pieces connected to an electrical source like a battery to zap the vermin when it touches both pieces together. Constructing a homemade rat zapper trap is not an easy task since you are dealing with wires and electricity. Unless you are a qualified electrical engineer, getting a commercial rat zapper will be a much better option over building one yourself.
Attach a metal plate or piece of tubing to a piece of wood or other material that won't conduct electricity. This makes up the back wall of the trap. If you use a tube. you can place the bait for this trap within the tube. Dry cat or dog food is often the best type of bait to use.
Construct the floor of the trap by placing a metal pad on a non-conductive board about one to two feet long. Leave at least 2 inches of the board uncovered by metal and connect that end to the back wall piece. You want enough space between the metal pieces so a rat's body will touch them together, but the bait won't connect the pieces if it's lying on the floor.
Connect the metal pieces to a 6 to 12-volt battery. One piece connects to the positive terminal with a wire and the other piece connects to the negative terminal. You should have to solder the wires to the metal pieces, making this the most difficult task of construction. The batteries should send an electric charge through anything that touches both metal plates at the same time.
Build or find a cage to place the electric trap in. It should be long enough for the entire trap floor to lay in, which will help prevent larger animals from reaching all the way to the back and getting shocked. It should also be narrow so a rat can't wander around in it without touching the metal floor.
Cut out the back wall of the cage so it can be removed and replaced easily. This is to give you easy access to the battery that will be stored between the trap's back end and the cage's back wall. From here, you can disconnect the battery from the wires if you need to disable the trap and change the battery. The battery usually needs to be changed for every ten rats killed.
Always protect yourself with rubber gloves and other forms of insulation when handling wire and electricity.