Warmth.
Heat is the simplest of the three. And the oldest. Warming a stiff knee helps the muscles around it feel more relaxed. It's not a cure. It's why your grandma kept a hot water bottle. It works the same way under a wrap.
Gentle massage.
The second piece. A steady, soft buzz around a sore spot helps tight muscles feel less tight. Not as strong as a massage gun. More like a good massage chair, made small enough to fit one knee.
Red light.
The newest piece. The one most people don't know. The 660nm and 850nm red light is used in lots of at-home wellness gadgets. It's not a cure. It's part of the routine. The point isn't what red light does on its own. It's that you get three kinds of comfort working at the same time — instead of just one.