system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do gas station pumps know when to stop?
gpt
Taken straight from Wikipedia - "Most modern pumps have an auto cut-off feature that stops the flow when the tank is full. This is done with a second tube, the sensing tube, that runs from just inside the mouth of the nozzle up to a Venturi pump in the pump handle. A mechanical valve in the pump handle detects this change of pressure and closes, preventing the flow of fuel."

I think that's a fairly basic explanation.. Unless someone else wants to take a crack at simplifying it further.