For my treadmill: Who cares? If my maid is evil and reporgrams my treadmill to randomly throw me off, there's a dozen more effective and hard to detect ways she could set traps in my house, like setting up common household cleaning products to mix and fill the house with chlorine gas.

Evil Maid attacks are real, but you don't need perfect security for your household appliances.

A device-specific "owner password" would be fine. Physical access is not proof of ownership, so there is no need to open the device up to trivial "evil maid"-style attacks. Of course some owners will lose their passwords, so some provision would need to be made to ensure that owner-access is not permanently lost.

There is a new technology that I learnt of recently. It’s called paper. It can be used to create instruction booklets or, by adding glue, it can become a sticker. We could print those keys on it.