A smart refrigerator can use what to detect when you are running low on milk, and then send a reminder to you on a wireless.

RFID scanning or Barcode reader

Explanation

Smart refrigerators have inbuilt RFID scanning technology that help monitor the stock that is inside your fridge. Once you pass your items through the inbuilt RFID scanner in the fridge, the barcode of your items is cross-referenced with a database and given a unique tag for identification. This technology helps detect and track the stock that is inside your fridge and when you start running low, the RFID can be triggered to send a reminder as a notification on your email or a text message.

answer; always; never;