Refrigerator door open/closed recognition device

A door open/closed recognition device configured to be attached to a top surface of an exterior of a refrigerator to be used, comprising:

• an attachment portion that comprises a magnet, a suction cup, or a double-sided tape provided on a bottom surface of the door open/closed recognition device and configured to fix the door open/closed recognition device on the top surface;
• a wireless communication unit that performs a wireless communication with a communication terminal;
• and
• a door open/closed recognition unit, wherein
• the door open/closed recognition unit includes:
• a sensor that has a detection area at a front surface of the refrigerator in a state where the door open/closed recognition device is attached on the top surface and that is configured to detect, from the top surface, an object which exists within the detection area at the front surface of the refrigerator;
• and
• a processor configured to recognize an open or closed state of a door of the refrigerator based on a detection result of the sensor,
• the door open/closed recognition unit is configured to recognize that any door of the refrigerator is in the open state or all doors of the refrigerator are in the closed state, based on a difference of a detected data that is output from the sensor.