The Leech Plug is a concept design by Conor Klein. The Leech mimics the behaviour of its namesake, once it has let the device connected to it to have its fill of electricity, the plug physically disconnects itself from the power supply.
The Leech Plug has been designed to help alleviate the problem of power drain. All devices when plugged into a socket continue to pull small amounts of electricity, chargers for devices such as phones keep taking these small amounts of electricity even when the device plugged into them is fully charged. These small amounts add up to quite a large problem and remembering to remove the chargers from a power supply can often be a lot of hassle and need continuous checking.
The Leech Plug concept idea is that by using a mix of a timer circuit and electromechanics you can get a plug to drop its cord once the device has been charged fully. The plug fits into a normal socket, with a cord to a plug socket to be used by the charger. The Leech can then drop this line when needed, physically cutting the device from the power supply and so stopping any additional electrical draining.
The only real problem with this idea is having to go around and plug the cord back in again when a device needs charging, or having dropped leads everywhere. However with some consideration to how it works the device should work well in any household, and would stop a lot of unnecessary electrical usage.
Source: Engadget