Listen in without blasting the TV or stereo system to tell what's going on. If you or someone you know is hard of hearing, these could keep the peace in the house by balancing everyone's needs between the volume up and the volume at normal levels that allow you to think. Or, another option might be if you have a baby in the house but don't want a headphone cord draped across the room, you can still watch movies on your big TV screen.
These three options are Sennheiser Listen Systems and each has it's own unique features--and pricing. The other great option is that their base design doesn't screen "assistive listening device!" and can be easily integrated into your current tech setup.
The version on the right, the 810 and 820 series, also sport infrared technology, allowing you to tuck the base away behind the cabinet and have it still function through furniture. The systems range in price from about $100-$230 and shopping around can pay off with savings.