I was very intrigued by the Dead Drops project (http://www.deaddrops.com), and as I was reading some of the comments, I came across one that said "I can't wait until someone hooks a car battery up to one of these. Then I'll be screwed". Well, I would be screwed too, so I decided to make a simple USB device to test for the presence of any current. The device has different volumes and tones, and the higher the volume and pitch, the more voltage. It has a max of 20V, which should be sufficient. Still, it would be better to pop one of these on a USB drive wired into an outlet as oppose to frying your nice little netbook.

To begin, gather the following supplies:

1 USB extender cable (Staples or RadioShack)

1 Piezoelectric Buzzer (Found at RadioShack)
=OR=
1 LED of choice, I wouldn't use them because they can't take as much voltage, unless you get some with very good resistors, which I have plenty of, but may be harder to find. In the following steps, just substitute an LED in for the buzzer, and it will all make sense.

Some solder (Your garage, or RadioShack)
A soldering iron (Your garage, or RadioShack)
Roll of electrical tape (Get 3M, high quality and well made. Your garage, or a hardware store)
5 minutes (Find some somewhere)

Step 1: Cut and Strip the Cable

Start by cutting off the male end (end you plug into your computer), and put it aside for use on another instructable or project.

Move your cutting implement down to the other end (female), and measure 1.5 inches from the base of the USB plug, and make a cut.

Then, measure approx .5 inches from the end of the cable, and cut/strip off the insulation, until you can see the red, black, green, and white wires. Cut off all excess rubbish on the cable.

Next, CUT OFF the green and white wires. Those are useless, as they are meant for data, not for power.

Now that those have been removed, strip the red and black wires, so they are exposed.

Take the buzzer, and cut the wires to a desired length, then strip them as well.

Step 2: Combining the Components

Put red to red, and black to black, and twist the wires together. I soldered them for an extra measure of strength, but that is optional. I highly recommend it though, just to keep the wires in their place.

Next, wrap electrical tape around one exposed wire, to insulate it properly. Then, run the electrical tape around the already taped wire, and the untaped wire, to combine them together snugly.

Step 3: Final Touches

Fold the wire backwards, and place the buzzer on top of the USB plug. Proceed to wrap the device in electrical tape, starting with the cable part so you don't have to hold it under pressure. Don't cover up the hole for the buzzer, as the volume of it may be reduced. Wrap it all up nicely, and make it look awesome.

Thanks for reading this, and I hope this device will one day save your computer! (haha)