How to Make an Alarm for Stairs

Fold a piece of cardboard lengthwise until it forms an elongated "V."

Secure a piece of aluminum foil along the length of one side of the folded cardboard. Then secure a second piece of foil to the other side the same way. Glue the foil to the cardboard if you really want them to be secure, but it's probably sufficient just to wrap them tightly. The two pieces of foil should come into contact when you fold the halves of the cardboard together.

Remove the insulation from both ends of the three pieces of wire. There should be about 1 inch or so of bare wire showing above the insulation.

Connect the end of one wire to the negative terminal of the 9-volt battery clip and the other end of the same wire to the negative terminal of a compatible alarm or buzzer.

Use electrician's tape to connect the end of another piece of wire to one of the tinfoil pieces. Then do the same thing with the last remaining wire and the other piece of tinfoil.

Connect the free end of one wire to the positive terminal on the battery clip.

Attach the free end of the last wire to the positive terminal of the buzzer.

Add a 9-volt battery to the clip, and place the buzzer and the battery flush against one step. If you have a rug or padding, cover them up. Otherwise, just make sure they're unobtrusive and won't get stepped on.

Place the cardboard with the wires attached to it on one of the stairs. Cover it with a rug or padding if you can, but only do so if the rug isn't heavy enough to cause the two pieces of foil to touch.

Test the alarm. When you step on the cardboard, you will press the cardboard together. When the pieces of foil touch, it will complete a circuit and cause the buzzer or alarm to go off.