Key features of a coffee mug heater include:

1. Heating Element: The device has a built-in heating element, commonly made of materials like ceramic or metal, that generates a controlled amount of heat.

2. Temperature Control: Some coffee mug heaters come with adjustable temperature settings, allowing users to choose their preferred level of warmth for their beverage.

3. Indicator Lights:  mug heaters have indicator lights to signal when the device is actively heating or when it has reached the set temperature.

4. Safety Features: To prevent accidents or overheating, these devices  include safety features such as automatic shut-off mechanisms after a certain period of inactivity.

5. Non-Slip Surface: The top surface of the heater has a non-slip material to securely hold the mug in place.

6. Compact Design: these heaters have a compact and slim design, making them easy to store and transport.

7. Plug-and-Play Operation: coffee mug heaters are easy to use, requiring only a standard electrical outlet for power. Users simply place their mug on the heating surface, and the device starts warming the beverage.

Coffee mug heaters are especially popular among individuals who enjoy sipping on hot beverages slowly, as they help maintain an optimal drinking temperature over an extended period. They provide a convenient solution for those who want to avoid the inconvenience of repeatedly reheating their drinks in a microwave or on a stovetop.