This video by Shane Ormonde discusses the low power magnetic hold and release mechanism:
With the inductor and magnet combined, ferrous metal objects can be held without any power indefinitely. To release the metal object the magnetic field holding it up needs to be temporarily cancelled out. This happens by pulsing current through the inductor which generates a magnetic field separate to that of the magnet. These two magnetic fields are of the opposite polarity meaning the inductors field cancels out the magnets field. The inductor only has to be powered long enough for the item to drop which I haven’t measured but its probably somewhere in the hundreds of milliseconds lets say around 100 milliseconds at a guess. This means you can hold an object for potentially a very long time (months, years maybe I dunno!) and expend a relatively small amount of power releasing it compared to if you’d used an electromagnet to hold the thing up which required a constant power source.
Details at Wattnotions.