Other days, other eyes
Oh whoop-de-doo! Bob Shaw's prediction comes one step closer.
Here we have a completely inert device, that is indetectably small and cheap enough to produce by the billion. Let's just wait for a version with a MEMS microphone (I suppose a camera is too much to ask for?) and you have the perfect bug. Better yet, it can be remain in its inert state for years, until needed.
It can be spread around like fairy dust, it won't transmit until it's illuminated by an RF feed and even if your bug-hunter discovers one - or ten - or a thousand in a room, it's a fair bet there will be many more not found. Even if "they" get them all, a couple of minutes will see a whole new batch introduced through the air-conditioning system. Or accidentally carried in on the clothes of people entering the room.