With all the high tech stuff on here I thought I'd do a reminder of keeping it simple. its uninsulated and I wouldn't trust it with more than a car headlight bulb 12V 5A.it's most certainly not waterproof.
Step 1: Materials
a wooden clothes peg. 2 drawring pins if you can get brass ones without the plastic coating so much the better. hook up wire of choice I've be used a twisted pair salvaged from somewhere for illustration.
Step 2: Remove the Plastic Covers
if you've got plain brass pins skip this step. hold your pin in the peg to keep your fingers away from the blade and split the plastic off with your cutting tool of choice.
Step 3: Insert Pins
open your clothes peg insert pin between jaws close the peg (watch your fingers if the pin is longer than the thickness of the jaws) repeat on other jaw
Step 4: Remove the Points
if your pins were long enough to come through the jaws. clip the point off with side cutters and or file smooth.
Step 5: Alternative Method
disassemble your clothes peg. insert the pins in the jaws. reassemble the peg
Step 6: Attach Wires
it is easier if you wrap the bare end around the pin before you push it in place. other wise you have to prise the pin out a little then hook your wire under the pin head and push it home again. I've hook the twisted pair under one leg of the spring just to keep it tidy.
Step 7: Put to Use
as a burglar alarm wedge open between door and frame when door is opened switch closes activating alarm. or as a trip line this requires an additional part.
Step 8: For Trip Line
to use as a trip line you need a small insulator. I've used a strip cut from a plastic card from junk mail. Any hard smooth plastic will do so would a wooden lollipop stick or coffee stirrer. file notches or drill holes so your line doesn't slip when tied on. knock a panel pin into your chosen support and install switch and trip line.