Can you add switches to a detached garage without running wires?
If your garage gets its power from the house (not from a separate electrical service), use an X10 switch and module. You’ll need to mount and power the X10 switch in a new electrical box somewhere in the house. Then install an in-line X10 relay in the electrical box where the appliance or light in the garage that you want to control gets its power. (We used the Leviton No. 6375 fixture relay 15A, available online) The X10 switch operates the electrical device by sending a signal throughout the household’s electrical system.
If you want the utmost in energy savings, buy an X10 switch with several buttons. (Shown here is the eight-button scene control keypad with dimmer, Insteon No. 2486DWH8, available online.) Then connect all your garage’s electrical devices—heater, small refrigerator, portable tool battery chargers, etc. (or anything else in the house)—to their own X10 modules. Turn on the heater and the fridge an hour before you plan to work out there.
Turn off the power to the switch and outlet at the circuit breaker box before installing the switch or relay.