I did have an app on my phone that put it into airplane mode, turned on the microphone and recorded what it picked up, whilst displaying a fake turning off screen. I used to nonchelantly put my phone on the desk during a meeting so they could see it "powering down". Great app that I can't remember the name of, but I ended up replacing it with a spy usb stick. No-one ever suspects USB sticks left lying around, or in your pocket. They both came in very handy when dealing with a toxic line manager trying to cover up his incompetance.