I'm currently building a world centered around a city. This city's main export, currency, and source of power are little metal orbs containing energy. Basically, it's the only place in the world where those are produced, and everyone in the city needs some.
They're not only used as money would be (buying food, clothes, and other stuff, and being received as salary), but are also necessary for lights, ovens, means of transportation, etc... to function. Think of it like batteries being used as money. A working citizen usually earns enough for him to power his house, and buy what he needs to live with the rest.
I've established that producing those orbs require levels of heat unbearable for organic beings, so people living there built robots to work in the furnaces in their place. Those robots are obviously powered by those same orbs, and are humanoid in structure (a head, two arms with hands, two legs, bipedal stance).
Now I'd like to have those robots become sentient thanks to the energy inside the orbs: people know how to manufacture and use them, but don't quite know how they really work, deep down. For the sake of simplicity, assume those robots acquired conscience thanks to the orb's magic.
My question is, how can those robots and ONLY those robots acquire sentience, but not the rest of the city's commodities (lights, vehicles, advanced tools, etc) since they're powered by the same orbs ?
The fact is I'm building it for a game and those robots are meant to be playable. It would kinda be a mess (although a hilarious mess) if players were able to play as a walking, talking oven.