You bought four smart switches. You turned off the breaker, pulled the old switch out, and found two wires and a ground where the instructions clearly show four. That is a switch loop, and it is the single most common obstacle to smart lighting in older homes.
What is actually in the box
A traditional switch only needs to interrupt the hot conductor. Power in, power out to the fixture, done. The neutral never has to visit the switch box at all, so in plenty of homes it does not. Builders ran the cheapest compliant configuration and moved on.
A smart switch is different. It contains a radio, a processor and often an indicator light, and all of that needs power continuously, even when the light it controls is off. To draw power continuously it needs a complete circuit, which means it needs a neutral.
How to know before you buy
Turn the breaker off, remove the switch plate and look into the box. You are looking for a bundle of white conductors joined with a wire nut and pushed to the back. That is a neutral, and you are in luck. If all you see is two conductors attached to the switch plus a bare ground, you have a switch loop.
One caveat: in some older installations a white conductor was used as a hot in a switch loop, sometimes marked with black tape and sometimes not. A white wire connected directly to the switch is not a neutral. Do not assume based on colour.
The three solutions
1. Pull a neutral to the box
The proper fix. We run new cable from the fixture or the nearest junction point to the switch box. How hard this is depends entirely on access: attic above the room makes it straightforward, a switch on an interior wall of a single-storey house with a slab and no attic access makes it work.
2. Use a no-neutral smart switch
Several manufacturers now make switches that work without a neutral, trickling a tiny current through the load to stay powered. These work well with the right fixtures, but can cause LED bulbs to glow faintly when off or flicker at low dim levels. Some require a bypass module installed at the fixture.
3. Move the smarts to the fixture
Put smart bulbs or an in-fixture module in, and replace the switch with one that never cuts power. Good for a single fixture. Less good in a house where anyone might flip the switch off and break the automation, which is every house with more than one occupant.
Three-way switches make it harder
If two switches control one light, both need attention. Most smart switch systems handle this with a main switch plus a companion, wired differently from a traditional three-way. Traveller conductors sometimes get repurposed. This is where DIY installs most often stall, and it is worth having done properly.
The other smart home wiring problems we get called about
- Video doorbells that drop offline. Nearly always an undersized doorbell transformer, not a defective camera. The transformer is usually in the attic or beside the panel and is a straightforward upgrade.
- Smart thermostats needing a C-wire. Older furnace wiring often has no common conductor. We either pull one or fit an adapter at the air handler.
- Cameras on batteries. Hardwired or PoE cabling ends the recharging cycle permanently.
- Wi-Fi dead zones. Access points need power where the signal needs to be. Running PoE to a ceiling location beats another mesh node on a shelf.
Doing it once
If you are planning smart lighting for a whole house rather than one room, it is worth having neutrals pulled to the switch locations properly rather than working around the limitation device by device. It costs more up front and stops the compatibility whack-a-mole permanently.
See what we cover on the smart home wiring page, or call and describe what you found in the box.