Recently we bought an Air Wick Colour Changing Candle, and was intrigued to find out how it worked.
We waited for it to burn down and found this:
After some experimentation, we found that pointing a TV remote at it also activates it:
From this, we were able to ascertain that it operates by detecting IR (infrared) – the black-coloured thing that looks like an LED is actually an IR receiver.
The fun never ends 😀