Electric can opener puzzle

[Wade Garrett]

How does my $10 counter-top electric can opener know to stop after the can rotates 360 degrees and the lid is severed all around and sticking to the spring-loaded magnetic arm?

I don't see any kind of sensor or probe and the rotation can't be time-dependent because it works with different diameter cans.

So how?

[RonNNN]

The magnet is holding down the "run switch" until it (the lid) lifts from the can.