Here's a how-to guide on removing the keysense plug from the key cylinder and get rid of the warning beep when you open the door with the keys left on the ignition.
1) Remove the plastic housing of the key cylinder by slightly pressing the points in the red circles:
2) Next, pull it all the way down to uncover the cablings and connectors (sorry for the unsteady shot...):
3) Locate the keysense connector. It is right next to the cylinder (mine had white and blue wires).
4) Pull down the connector gently (pull the connector, not the cables!)
5) Just as a precaution, put some insulating tape around it.
6) Put the cover back and you are ready!
Thanks for reading.
NOTE: Toyota Owners Club cannot endorse or condone the removal of any safety systems.
Users should consider the above before following the guide as it may have adverse affects with your car insurance.