Or maybe the word was subverted after it was chosen to represent this concept? Not saying it was the case (I don't know) just mentioning the possibility.
Most modern domestic smoke detectors are now photoelectric, rather than ionization based.
Not only do they not contain toxic Americum 241, photoelectric smoke detectors are also both more sensitive to real fires and less prone to false alarms.
(The later is actually really important, as people will often disable smoke detectors in response to a false alarm - and then forget about them)
We had a kitchen smoke detector in college that was kept swaddled in plastic wrap at all times because it went off every. time. we tried to cook something. Absolutely a safety hazard, yeah.
Seems to me that if you use compressed air to displace water within the sphere, you could actually store more energy this way... That would require the air to drive electric generators when the sphere is being filled with water though.
Once you start compressing and decompressing air you get a lot of heat loss though, that I would imagine isn't as much of an issue when you're just pumping plain water back and forth