This is a very simple photosensor-based system that alerts the user when the refrigerator door is left open.
This device measures the temperature of the room. When it is above a specified temperature a LED will be activated to let you know.
Do not be discouraged if you are not a green thumber! Here is a watering system that can account for complex human lifestyles.
Set up a device in your cabinet to notify you when to wash your dishes. This device requires the Particle Argon or Photon.