The author used to employ a switching central that allows mains appliances among his PC equipment to be individually switched on and off by pressing pushbuttons. One of these pushbuttons switches the PC on and off. Good economics, but not perfect, because awkward situations can arise when a wrong pushbutton is pressed, causing the PC to be switched off instead of, say, powering up the printer.A solution was found in the use of relay which is switched on and off only if the relevant pushbutton is pressed twice within a certain period. The first press causes a LED inside the pushbutton to flash for about 7 seconds. If you press again within this period, the relay is energised and the LED lights permanently. The switch-off procedure is identical. In this way, the switch is given a level of security.