My girlfriend's grandmother recently had surgery on her foot, so she uses this system to hear when she's called for help.
Each part is completely across the house from the other--she listens from the living room, most often at the computer, while her grandmother keeps her foot propped up in the bedroom. The volume control on the right side lets you go from silent to easily loud enough to blare over a loud TV. The sound itself is clear enough to understand what she says, although it is a bit fuzzy.
There are two lights on the front of the piece you listen in with. One lets you know how full the battery is, the other keeps track of the monitor itself.
You can also plug the system into the wall, thus preserving the battery life when you use it.
The flat bottom and handle on top ensures versatility and portability.