As promised, here is the break down of the Harbor Freight mat switch. You can purchase it online thru Harbor Freight's online store, item number 96481, or in their store. If you go to the store, be prepaired to hunt for this item. As you can see in the first picture below, it is in a plain white box. The only marking on the box is a small label noted as "Alarm Mat". I assume that most stores will have it in the housewares section as mine did.

In the box, you will find the 21"x14" black plastic mat, the 105 decible alarm, 2 screws and drywall anchors, and the documentation. On the side of the alarm box, you have your choice of Alarm, Off, or Chime; and is powered by a 9 volt battery. The alarm box connects to the mat using a simple slide in connector, which contains 2 conductors. During my testing, I found that I needed to cover the speaker with my hand. This sucker is loud! O'yea, almost forgot; in one of the pictures below, I have placed a normal kitchen napkin in the middle of the mat to give everyone an idea how big the mat is.

To test the mat, I started out by pressing on the edge of the mat and worked my way inward until the alarm sounded. The alarm didn't sound until I was about an inch in from the edge. This was fairly consistant the whole way around the mat. Some spots seemed to activate the alarm a little easier than others, which I found out why after I cut open the plastic cover.

With the cover removed, you can see that the insides are nothing more than a couple sheets of paper with a metal type coating on the inside. The two conductors are soldered to the sheets, one on top and one on bottom. Seperating the paper sheets is a 1/8" sheet of foam. Throughout the sheet, are about 1.25" circle cutouts that allow for the completion of the circuit. The sheets are held together along the edges with clear tape.

I found that once all the air was out of the inside, it fit rather nicely under a welcome mat and worked witout issue. The product isn't the greatest, but for the price, I think it is a great buy. I paid $7.99 for the one I purchased with the "preferred member" coupon, normally $9.99. That's pretty much about it.

Info Added : 8/25/08

Per request, I have added a drawing representing how to use this to trigger a prop. I don't know the specifics on what is required to trigger the prop, so the picture is only intended to represent how to connect the pressure mat to a standard 5 volt relay.

Basically, you would disregard the alarm portion of the package. You will not need it. Take the pressure mat and cut the connector off the end of the wire. Seperate the two wires apart about an inch or so and strip the insulation off the wire ends. Next take a wall wart (one that is appropriate for the voltage relay you are using. In this example, I used a 5 Volt relay, so you would use a 5 Volt wall wart) and strip the insulation off the ends of the wires, just like you did with the pressure mat. Now take one of the wires from the wall wart and solder it to one of the wires from the mat. The other wire from the mat gets soldered to one of the coil pins on the relay. Finally, the second wire from the wall wart gets soldered to the other coil pin on the relay. What you should end up with is a big loop. Make sure you shrink tube or electrical tape the locations where you soldered the wires together so they don't short against each other.

You should now be able to test the your work. Plug the wall wart into the wall. Nothing should happen. Now step on the mat. You should hear a click from the relay. If you didn't hear a click, make sure you didn't mis-solder a wire or that something didn't come loose. All you need to do now is connect the other pins that form the contact closer to your prop. I am being specifically vague on this part because each user could have different needs on how to accomplish this.

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Harbor Freight Mat Switch