If you’re wondering about a vacancy switch vs occupancy switch, both types of switches have their uses. The basic difference comes down to whether you want the light to turn on when it senses motion and turn itself off after the last time it senses motion, or only turn itself off after the last time it senses motion.
An occupancy sensor turn lights on automatically when it detects motion, then turns the lights off automatically soon after people leave the room. This is good for kitchens, bathrooms, and the living area of the house.
A vacancy sensor doesn’t turn lights on automatically. You still have to turn the light on when you enter the room. But it does turn the lights off automatically soon after people leave the room. This makes it good for rooms like bedrooms. In bedrooms, you want the lights to go off if someone forgets to switch them off. But you don’t want the lights turning on in the middle of the night when someone rolls over in bed.
Most occupancy switches have a vacancy switch mode that you can activate. Often it’s just a matter of pushing the button a certain length of time and watching the light flash to verify what mode it activated. The instructions will be in the paper manual that comes with the switch. When I use a Lutron MS-OPS2 switch in bedrooms, I activate the vacancy switch mode. It still works for saving energy in that mode. It just doesn’t automate both aspects of lighting.
By switching to motion-sensing switches and high-efficiency bulbs, I was able to cut my electric bill by 19 percent. So I like and definitely recommend motion-sensing switches. The key is just knowing when to use them as occupancy switches and when to use them as vacancy switches so they make your life more convenient, not more annoying.