Minimal tools reqired:
Exacto Knife (Stanley knife)
Step 2: Take Appart the PIR sensor
Take apart the swivelling part and take out the the back circuit board (the power board)
Step 3: Solder the wires up
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
Close up the PIR sensor and mount both in the position of choice with a mains connection as said in the instructions.