Vendor Lock-in

I own two Uninterruptable Power Supply units. Each has a button on the front with which you can perform a self-test; I do this once a month to make sure that they are "still good".

On unit A, you tap the button and it does a self-test. If you press and hold the button then the unit turns off, taking the attached hardware with it.

Unit B (from a different vendor) requires you to hold the button in to perform the self-test. Tapping the button… no, why don't you guess what that does?

Sneakiest attempt at vendor lock-in I think I've ever come across.