Two less vital things before we proceed.
One is, that some gadgets we mentioned (e.g. the door lock) have two power sources (a primary and a plan B); the "power controller" part then gets inevitably more complex, having to handle both and switch between them as appropriate. Also, some gadgets have several functions, with different power consumption and different priorities for scheduling/permanent or intermittent powering - this is for example the clock, with timekeeping part (RTC), display and control, and radio receiver for precise time setup.
The other thing is an unrelated idea or question: having mentioned mechanical power source, what amount of energy can we talk about? Let's push things a bit to the edge: say having a 100kg weight running all the way from attic to cellar, say 10m, can it power a clock for a century?