Now pop the red lens out. Just slide a fingernail under its edge and pry. It comes out easily.

Actually, you don't have to remove the lens. You can leave it where it is. Originally, I thought there was an LED that protruded into the lens from the circuit board, which you could break off if you didn't remove the lens before removing the circuit board. But it turns out that there is not an LED there, just a tiny transmitter, which doesn't protrude into the lens.