Designed in Israel by a military contractor, the Pro Extreme Contact Microphone enables you to amplify the sound being produced behind walls, ceilings and floors, thus making holding up a glass cup to a door obsolete. The acoustic "super sensor" amplifies sounds by up to 100 times thanks to the 1-watt RMS amplifier. Additionally, the included headphones include active noise cancellation. Popularized by Bose, active noise cancellation attempts to cancel out unwanted, exterior sounds by neutralizing sound waves via deconstructive interference.
Just think of all the mischief you could carry out with this. Why, you could spy on your bratty sister, spy on your bratty brother, spy on your authoritarian parents, etc. More realistically, it can be used to determine the location of a pest's nest or where a broken pipe is, provided you pony up $395.