Step 1 – Apply one side of the 2-way adhesive tape to the wide edge of the magnet. Place the magnet on one edge of the interior broad side of the door, ensuring that the magnet does not interfere with the door closing.
Step 2 – Remove the lid on the plastic box. Use the pliers to bend the leads on the inductor, so that the leads are at a 90-degree angle to the inductor body. Place the inductor body against one of the inside box walls. Face the inductor leads towards the inside of the box. Tape the inductor to the box wall using the electrical tape.
Step 3 – Use the pliers to cut a 4-inch piece of red wire. Strip 1/2 an inch of insulation from the ends of this wire. Twist together one end of the wire with one of the inductor leads. Use the soldering iron to melt a small drop of solder to this electrical joint, and smooth out the soldered joint with the tip of the soldering iron until the joint is shiny and free of lumps. Wrap the exposed metal parts of this electrical joint with electrical tape.
Step 4 – Twist together the loose end of the stripped red wire jointly with one of the leads from the 470-ohm resistor, and with the red lead from the battery snap connector. Solder this electrical joint and wrap the exposed metal parts of this joint with electrical tape.
Step 5 – Twist together one of the leads from the buzzer with the loose lead from the 470-ohm resistor. Solder this electrical joint and wrap the exposed metal parts of this joint with electrical tape.
Step 6 – Twist the collector leads from both resistors together jointly with the remaining lead from the buzzer. Solder this electrical joint and cover the exposed metal parts of the joint with electrical tape.
Step 7 – Twist together the emitter lead from the first transistor together with the base lead from the second transistor. Solder this electrical lead, but do not wrap it with electrical tape.
Step 8 – Twist together the base lead from the first transistor with one of the leads from the 100-kiloohm resistor. Solder this electrical joint and wrap the exposed metal parts of the joint with electrical tape. Twist together the remaining lead from this resistor with the remaining lead from the solenoid, solder the electrical joint and cover the exposed metal parts of this joint with electrical tape.
Step 9 – Cut a 4-inch piece of black wire and strip 1/2 an inch of insulation from the ends of the wire. Twist together one end of this wire with the emitter lead from the second transistor and solder this electrical joint. Twist together the loose end of this wire together with the black wire from the battery snap connector, and solder this electrical joint. Cover the exposed metal parts of both electrical joints with one piece of electrical tape each.
Step 10 – Place the box on the door frame parallel to the bar magnet. Ensure that the inductor inside the box is as close to the magnet as possible without interfering with the operation of the door. Drill a hole through the box wall that contacts the door frame and mount the box to the door frame. Cover the mounting screw with a piece of electrical tape. Attach the battery to the battery snap connector and tape the battery to one of the inside walls of the box. Replace the lid on the box.