You can actually hear the Touch ID sensor on the iPhone 6 and 6 Plus
It’s odd to think about, but did you know that the Touch ID sensor on your iPhone makes noise? If you hold an iPhone 6 or 6 Plus up to your ear in a quiet room and touch the Touch ID sensor, then you will hear a very faint clicking sound emitting from the vicinity of the sensor. It’s just another weird fact gleaned from the /r/apple this morning.