These devices combine two functions. Correctly installed they are just as safe as two individual switches. Combination switches are always installed with through-switch wiring and never with end-line wiring. That means two or three cables enter the box.
Shut off power to the circuit before removing the old switch. To be sure that rebent wires do not break, cut and restrip the wire ends before you connect them.
Your choice in combination switches was once limited to a switch and a receptacle or switch and a switch. These days, you have many more possibilities: Remote controls, switch and dimmer, fan and light controls to name a few.
About 30 minutes to remove an old combination switch and replace it
Screwdriver, side cutters, strippers, long-nose pliers
Stripping wire, connecting wire to terminals
Lay a towel or small drop cloth on the surface below the switch.
Combination switch, electrician's tape, wire for pigtails
Squeeze two switches into the space of one. Three cables enter the box: One brings power, the other two run to separate fixtures. Connect the grounds and splice all the neutral (white) wires together. Attach the feed wire to a terminal with the connecting tab. Connect the other two black wires to terminals on the side with no tab.
To make the plug always hot (not controlled by the switch) on a switch/receptacle, splice a pigtail to all the neutral (white) wires and connect the pigtail to the silver terminal. Connect the power wire to the brass terminal with the connecting tab. Splice the grounds. Attach the black wire from the switched fixture to the brass terminal with no connecting tab.
To have the switch control a middle-of-run receptacle, connect the grounds. Make a white pigtail and connect it to a chrome terminal on the side of the device that doesn't have a connecting tab. Splice all the white wires together. Attach the black feed wire to the brass terminal that is not attached to the connecting tab. Attach the outgoing black wire to one of the black terminal screws next to the connecting tab.
When you replace a light with a ceiling fan, the old switch will still turn the fan off and on. To control speed and light levels without significant rewiring, however, you can use a remote switch. A wall-mounted remote looks like a normal switch but lets you adjust both fan speed and light level without rewiring.
This hardwired switch lets you adjust up to four fans and their lights from a single switch. Replace the existing switch and attach a module to each fan. The switch and module allow you to adjust fan speed and dim lights without having to run new wires from the fan to the switch.
This is a variation of the old switch/receptacle combination. Because GFCIs don't work if they're switched on and off, the switch on these units is meant to control other things, such as lights or exhaust fans in areas that require a GFCI. The switches are available in a wide variety of styles, including a device with two switches and a GFCI.
Walk into a room and the light automatically turns on when this switch is installed. It remains on for a length of time you select. When the time is up, the lights go out -- as long as no one is moving in the room. A manual override lets you turn the light on and leave it on for as long as you like.
Sophisticated lighting schemes call for more switches. It's not unusual for a room to have two or three sets of lights, each controlled by its own switch. A line of switches on the wall can detract from the room's style. Traditional double switches cut the space consumed in half, but triple switches are even better.
There are times when it helps to know that you really did flip the switch. Did you remember to turn off the garage light? Is the on-at-dusk light going to come on at dusk or did you accidentally flip the cutoff switch? Check the pilot light. If it's on, so is the power.