Buddhism

Alright it's a bit far fetched but bear with me. Back in the olden days, people would use nails driven in a candle to measure a certain amount of time. As the candle melts, the nail would drop on a metal tray and make a sound.

So you'd need to get a candle of your choice, preferably a stick candle. Burn it for your ideal mediation time and measure by how much it melted away. Then get a nail, drive it into the candle, according to your measurement. Perhaps not too far in the candle, enough for the nail to stay put but shallow enough to drop easily when the wax gets liquid around it. Pop the candle on some metal tray, light it, take a deep breath and close your eyes. When you hear a clang then you're done. But keep going if you are enjoying it!