These candle snuffers are a neat idea that allow you to automatically extinguish a candle after a predetermined time interval. Simply slip the device onto a candle, and the spring loaded cap or lid will automatically be held in the open position. However as the candle burns down, there will come a point where the spring loaded cap will no longer be held open, and the spring will cause it to close, over the flame, and put the candle out.

You could use it to extinguish the candle after a set period of time, or as Tim suggests in the video, you could use these as a safety feature if the candles were placed in a wreath or decoration, and you didn't want the candle to burn down so far that there was a danger of setting the decoration on fire.