You're really not suppose to leave a candle burning unattended, but if you're too forgetful to blow out the candle, are you going to remember to set the timer? I don't think I would want my candles to suddenly go out by themselves. When I light a candle, I don't know exactly when I'm going to want to put it out. Unlike electric lights, candles put themselves out eventually anyway when they run out of wax.

Having said all that, I would say that it would be doable and such a product might even sell. There are lots of candle fanatics around who will buy any kind of candle related nicknack. Or it might be bought for them as a gift.

Making a gadget to actually blow out a candle is trickier than it sounds. As the candle burns down, the location of the flame moves down, so you have to figure out how to aim the blow at the right place. Sometimes, when you try to blow out a candle, it doesn't go out even though you blew quite hard. If you blow too hard, molten wax will get splattered around.

I'm not saying it couldn't be done, I could probably do it myself, but it would be a bit complicated. It might be easier to design a candle holder with a lid that automatically shuts to extinguish the flame instead. That would be simpler and more fool-proof.

I can see the benefit of this idea. It's not so much as a factor of simple forgetfulness (Show me a person that never forgot something). But covers a basic fact that defecation occurs. It could be conceivable to have a bottom layer of the candle be infused with co2 bubble around the wick or bubbles that when melted would extinguish the flame through suffocation rather than a forceful blast. Or a candle that will have a timed burn, lets say, it'll have the co2 bubble layer every hour or so of burn time. The self-extinguishing safety candle could make a decent selling point. However it could lead to complacency.

I just Googled and discovered that someone already makes an automatic candle extinguisher. Not surprisingly, it uses a lid that automatically closes, like I suggested.