How to Make an Alarm Bell

An alarm goes off when electric current completes a circuit between an electrical source and a device that make noise, for example, a bell. A basic, small homemade alarm that alerts you when a door is opened can be created with supplies from a hobby store. Household tools will be needed, but no special electrical skills. The portability of this alarm will let you take it with you wherever you go.

Electric wire, 16-gauge
Wire cutters
Tape measure
Wire strippers
Soldering iron
Solder
"AA" battery pack
DC-powered electric bell
Magnetic switch
Phillips-head jewelers screwdriver
Switch plate
"AA" batteries
Duct tape

Instructions

- 1
  Cut three 1-foot lengths of electric wire with the wire cutters. Strip 1/2 inch of insulation from both ends of each wire using wire strippers. Discard the cut insulation.
- 2
  Heat up the soldering iron for five minutes. Solder the end of one of the wires to the positive (+) labeled contact on the side of the battery pack. Let the solder cool for a minute or two. Solder an end of a second wire in the same manner to the battery pack, to the negative (-) labeled contact. Let the solder cool for a minute or two.
- 3
  Solder the free end of the wire connected to the battery pack's positive (+) labeled contact to the positive (+) labeled contact on the electric bell. Let the solder cool for a minute or two. Solder the end of the third electric wire to the negative (-) labeled contact on the electric bell. Let the solder cool.
- 4
  Loosen the two screws on the magnetic switch using a Phillips-head screwdriver. Wind the free end of the wire soldered to the electric bell around one of the screws. Wind the free end of the wire soldered to the battery pack's negative (-) labeled contact around the other screw on the bell. Tighten the screws.
- 5
  Place your homemade alarm on the floor, next to the door frame of the door that is to be alarmed. Open the door slightly. Remove the paper backing from one side of the switch plate. Place the adhesive side of the switch plate against the bottom inside door edge. Press the switch plate against the door to secure the adhesive.
- 6
  Remove the paper backing from one side of the switch. Place the adhesive side of the switch against the bottom inside door frame's edge, opposite the switch plate. Press the switch against the door frame to secure the adhesive.
- 7
  Close the door. Insert batteries into the battery pack. Tape the battery pack to the baseboard of the wall with a strip of duct tape. Tape the bell to the wall just above the baseboard with strips of duct tape. When the door opens, the alarm should go off--this movement activates the magnetic switch and sends electricity to the bell.

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