In the movie "In Time" a person stops aging when they hit 25. At that point their "clock" starts ticking, and the person no longer ages, instead they suddenly die when their time runs out.
How does this technology work? How does it stop a person from aging? Also: (Since it has to do with not aging, and is most likely connected) What kills a person when their clock runs out?
It doesn't happen because of the implant (the device implant - the clock), the device only ends their life (stops their heart).
It happens because of genetic alteration that allowed humanity to stop aging at 25. What this genetic alteration is has not been explained in the movie. It's probably some kind of genetic-chemical-electronic combination.
Since the device stops their heart, it probably stops blood flow through their heart, resulting in no oxygen supply to the heart, followed by death. It can also be explained by a heart attack that causes death or an instant electric shock through their heart - a frequency that causes the heart to stop beating.
This is addressed in the film's original script (back when the film was called I'm.Mortal) which offers a number of 'info-dumps' about the clocks that don't seem to have made it into the final cut of the film.
All of humanity has been genetically engineered.
In the not-too-distant future the aging gene has been switched off. (NB: The minor variation in the biological age of adults is due to the differing time of life an individual matures. Full maturation triggers the aging gene to switch off and the "body clock" to begin ticking.)
"Time" can be moved from person to person.
Time is transferred from person to person by way of a unique handshake. The right wrists are held together - the time conveyed by the electricity in the pulse. The one who has their hand on top of the other - who literally has the "upper hand" - is the one extracting the time. Both parties monitor the amount of time exchanged by watching the body clock on their left wrist.
Running out of time causes a heart attack.
In this world, the genetically rewired circuitry of the body that keeps you young is also what kills you. Suddenly Rachel suffers an irreversible shock to the system - a massive heart attack. She is hurled off her feet, dead before she hits the ground.
The clocks are biological, not technological.
Greta proudly shows off her newborn's wrist with its tiny but perfectly-formed unticking clock.
GRETA There it is.
We FOCUS on the digits indicating years - "1".
0001y:00m:0w:0d:00h:00m:00s
BOREL: Shame we've got to wait twenty years - we could use that year right now.
GRETA: It's a miracle, isn't it - how our bodies know when to switch it on? Nature sure is beautiful.
BOREL: Except it's not nature. We don't even know any more how our bodies do it. Why a year? Why are we even born with this clock?
