Time bomb

[Ioannis]

The idea is device dependent because it might be on a pic that is constantly on or constantly off (like a remote control).

Timer is one resource, times operated is another. EEPROM storage is the place to store our variable to check for... passing away.

Will come back with more practical ideas.

Ioannis

[pedja089]

You also can count how timer device is power on. Store that value in EEPROM.
And you can check some unused eeprom address. And if device is powered xy times, and value on that address is FF then STOP. When thy pay you, send them another hex with correct value on that address. Or just make some combination of button that must be pressed at power up to write correct value in eeprom, and unprotect device.