If we can cast a radio or electromagnetic wave through a micro magnetic coils with a tangible amount of friction producing energy to replace the job of a battery, this energy will be use to hit a micro gong that will produce a wakeup call and this may only be well build with inert elements

Or

Another possibility is to build a micro solar-signal device that will be embedded but will permit (highly sensitive to a negligible) ultraviolet rays to pass through the embedded surrounding to produce micro energy which will be impendence of the batteries.