Re: All sounds very plausible...
The ones I took apart were piezoelectric. The wire hammer was held under tension by a peg. When you operated the shutter a small plastic spade was pushed into the slot, forcing the wire hammer off its peg. It in turn swung hard against the center post of the bulb, generating the electricity needed to fire the cube.
A dismantled one once gave a friend a nice belt when he was playing with it.
For a while some stage magicians used them in conjunction with a hand-held gaff (bit of bent metal) as "invisible cameras".