Danger is my middle name and I wanted to make something cool and tech-y for the Halloween contest- we're budding engineers, so we figured we should be able to put together something cool.

What we came out with was this: a spider with eight LED eyes that flash on and off depending on the position of a couple of tilt sensors. It's perfect for looking innocuous, and then surprising passersby who brush by it, only to have it flash on at them.

We hung it above our dorm room door to scare visitors.

Step 1: Gather Materials

You will need:
-2 Tilt sensors (pictured below)
-8 LEDs
-some fabric
-a hot glue gun
-solder and soldering iron
-switch
-a ping pong ball
-some wire
-some kind of cord
-batteries for your LEDs & a battery pack
-electrical tape

Step 2: Solder the Circuit

Wire up LEDs to tilt sensors such that different LEDs are on and off depending on which way you tilt the two tilt sensors.

In ours, the first tilt sensor is before any LEDs are powered, so that there is a way for the spider to be on, but dormant. This is great for surprising people.

CAREFUL: make sure one end of each LED has a connection to ground, and the other to power. You can do this by wiring the ground side of all of the LEDs together and wiring them directly to the ground on your battery pack (bypassing the tilt sensors) and then connecting the other ends to power via the tilt sensors. We might have broken a couple of LEDs soldering this, so check your circuit before you connect power.

Add a slide switch between power and the first LED or tilt sensor.

Step 3: Bundle Your Circuit

Arrange your LED eyes and bundle each side with electrical tape.
Then bundle them together.
Then bundle the extra wire so it's compact.
Then tape together the tilt sensors so that they are perpendicular to each other.
Then tape that, and the batteries, and the switch all together (make sure the switch is on the outside.

Step 4: Make the Head

The head is made of a ping pong ball with two large holes in it: one for the circuit bundle to stick into, and the other, for the LEDs to protrude out of.

I used scissors to chip away at my ping pong ball.

Step 5: Cover the Head in Fabric

We used adhesive felt (because we had some lying around), but it was pretty stiff and hard to manipulate. Something soft or stretchy might be better. Anyway, make a hole in it (just a slit that you can poke the eyes through) and then shape and glue the rest so that it fits the head.

Step 6: Make the Body

Cut out some fabric as shown; sew together, leaving the front open.

Stuff partially with polyfill or other type of stuffing, leaving room for the circuit.

Step 7: Insert Circuitry

Make sure you know which side you want up- which orientations of the tilt sensors will give you your desired flash types.

Hot glue to head fabric.

Step 8: Make a Hole for the Switch

Ours came out the back; yours could go anywhere you put it. Hot glue around it so the stuffing doesn't show.

Step 9: Make the Legs

I used five pipe cleaners. Bend all of them in half to find the middle, then weave the fifth pipe cleaner so that it's centered on all of them. This should make a little fuzzy eight-legged flat spider.

Next, use electrical tape to make the legs black. In the picture below, I spiralled it around the legs. Don't do that. Fold the tape over the legs longways and you will use much less tape.

Step 10: Add the Legs

Hot glue the legs to the bottom of the body of the spider.

Step 11: Decorate (optional)

I added some fuzzy white fabric to give the spider some scary markings.

Step 12: Add Strin

I made a slip knot and pulled it around the butt of the spider.

We also considered tying it to the switch, but our flashing lights worked better at this angle.

There are lots of ways to attach string; pick your favorite. A simple slip knot seems to hold this one fine.