Wow! That's really cool. Just imagine that your car is getting serviced and It's done in such a way that you agree on a set amount of sats but you can expedite the service by competing with others to get the vehicle done. Imagine the shitshow!
The "relay/switch" could be triggered by the GPIO pins on a Raspberry Pi or similar SBC.
Search online "raspberry pi vending machine" there are hundreds of projects and dozens of guides.
If the computer has internet, it could run a LN node on the computer itself and send signal to the GPIO when the conditions are met (invoice paid). Or use an API to generate and check status of invoices on someone else's node (or remote node you control).
If the computer is offline, you can use this method to check if payment is received: