There is no microchip which means it can't be a listening/recording device. Seeing as the circuit is very simple, my bets would be on it being some kind of oscillator, as I can't see what else you could build using only two components. An oscillator circuit produces a single unchanging, constant tone. I know that circuits making high pitched tones are used to repel moles (in gardens) and teenagers (in shopping centers). I guess they could be used to repel, like, moths as well?
Edit: didn't notice the blank epoxy blob. Yeah that's a microchip