For this easy tripwire all you need is
Wireless transmitter/receiver (I just used a doorbell)
First take the peg and wrap a small amount of foil around both ends.
Now get you wire and tape it onto the foil end of the peg. (Do this on both sides)
Now get you transmitter and solder 2 wires on or just tape them on like this.
Now get your string and tape a small amount of wire to it and place it in the peg.
Lastly place the tripwire in you desired spot and wait, so now the transmitter receiver will be with you and will notify you when someone's on you property!