Review on ☕ Intelligent Gravity Sensing Smart Coffee Mug Warmer - Auto On/Off - Beverage Warmer Plate for Desk, Office, Home - Ideal for Milk, Tea, Chocolate, Water - White by Autumn Park

This device works exactly how I want a cup warmer to work: it turns on automatically when you put a cup on it and turns off automatically when you when you put it up you take out the cup. And it is powered by USB, which is very convenient. The problem is that it just doesn't get warm. The maximum temperature stated in the product description is 50°C, which corresponds to 122°F. This would be a good temperature for coffee (the ideal temperature for drinking is said to be 136F), but of course coffee is never as hot as it gets warmer - it's surrounded by air that's only around 72F. Assuming that the heating plate and the surrounding air have the same total conductivity, the equilibrium temperature of the coffee is 40 °C, which is lukewarm. It's better than cold coffee, but not by much. Too bad it doesn't heat because otherwise the design of this product is excellent. Also note that it doesn't get as much power when plugged into a computer's USB port, so it even works as a cooler. You need to plug it into an outlet to get the full effect.