If you want to know the temperature, simple analog sensors that you can attach and leave on various surfaces are (almost) a dime a dozen. Few, however, are as visually pleasing as this ESP8266-based sensor from “mcer12.” Besides displaying the temperature locally, it uses its WiFi abilities to publish temperature and humidity data, as well as battery percentage via MQTT.
The device features a small 3D-printed shell, containing the ESP8266 module, along with a 13x7 LED array. These LEDs are diffused by the print structure itself, which includes baffles to keep light separated into neat squares. A single interface button is made from a deformable tab in the printed case and a recession allows the SHT30 temp/humidity sensor to “view” the world around it, without being unintentionally poked.
The sensor unit can be affixed to surfaces via a magnet — or presumably any sort of adhesive — making it perfect for display on the front of your fridge. It’s designed to consume around 30-40µA of current when asleep, so it should last for months on a 400mA battery before MQTT announces it needs some extra juice. When that does happen, there's a TP4054 charger onboard for USB power transfer.