Omron has released such a thing: a manual mains switch with a coil inside that will flip it to the ‘off’ position following the application of 5V for 50ms. Unlike a latching relay, the coil cannot set it to the ‘on’ position.
There is also a more elaborate version, dubbed “delayed-off” (see below), for situations where power cannot be un-predictably removed – when data has to be stored first, or a machine has to be bought to rest, for example.
“The switch is a great asset in implementing systems that meet the requirements of the European Commission ErP Ecodesign directive,” said Omron. “It specifies that the power consumption of equipment in any off-mode condition shall not exceed 0.5W. In stand-by, consumption should also not exceed 0.5W, unless the equipment has a status display in which case 1W is permissible.”
Called A8GS, the switches look just like a normal mains rocker switches, and are rated for 16A at 125Vac and 10A at 250Vac (3mm contact gap, UL and cUL approved, EN conforming).
As contacts are silver alloy, there is a minimum load (5Vdc 200mA). For working below this, a gold alloy versions functions down to 3Vdc 1mA, and up to 5Vac 200mA.
This is not a great lump of a thing. It measures 30x17mm when seen from the front, and is 28.5mm deep from the mounting face to the end of its terminals.
Power contacts are SPST or DPST, and both power and coil connections are either all 4.8mm spades, or all solder terminals.
There are also versions where the coil is supplied through a 2pin connector (CT series from Tyco, or XR from JST). And there are all-manual versions without a coil.
For more detail: Rocker switch turns itself off