Sense People approaching up your drive with two pieces of cheap technology.
Minimal tools reqired:
Exacto Knife (Stanley knife)
Soldering Iron
Drill

Step 1: Parts:

PIR motion sensor
Cheap Radio Doorbell
Enclosure for the doorbell
Wire
Tape

Step 2: Take Appart the PIR Sensor

You only have to take apart the PIR sensor by unscrewing the axis clamp
Take apart the swivelling part and take out the the back circuit board (the power board)

Step 3: Solder the Wires Up

First find the relay (a large component (in the pic it is blue)).
Luckily the sensor circuit board runs off the same voltage as the doorbell.
Attach the two wires off the relay next to the sensor connections and use a multimeter to find - (should be the same as the blue wire.
Run the wires through the case of the sensor.
Solder the wires to the doorbell's battery connection.
Solder a piece of wire across the switch on the doorbell.

Step 4: Finishing It

Box the doorbell and seal with tape.
Close up the PIR sensor and mount both in the position of choice with a mains connection as said in the instructions.

Step 5: Test

When switched on The doorbell should ring when anything moves in its sensor area, it may work with cars also.

Step 6: Disclaimer

This instructable is submitted in good faith, playing with electricity is dangerous, you do this at your own risk, any damage caused is not the author's fault.