last night I dreamed about a company that takes a pint of blood from you, freeze-dries it, crushes it to powder, and then gives you an hourglass with your blood as the sand
it's a very large, very slow hourglass mounted on a base that prevents it from being turned over. the amount of sand pre-loaded in the bottom is based on how old you are, and the amount in the top is based on your projected life expectancy. a few grains trickle down each day.
there's no magical bond to guarantee your lifespan actually matches the hourglass, but it's... a reminder.
