Most smart switch projects stall at the same point: you open the first switch box, and there is no neutral wire. Here is why, and what the three real solutions are.
Why the neutral is missing
For decades, the standard way to wire a switch was a switch loop. Power went to the fixture first, and only the hot conductor was looped down to the switch and back. The neutral stayed at the fixture, because a mechanical switch does not need power to operate.
A smart switch does need power, constantly, for its radio and processor. Without a neutral it has nowhere to complete that circuit.
Solution one: run a neutral
The cleanest answer. If the wall cavity is accessible and the run from fixture to switch is short, pulling a proper neutral gives you a normal box that will accept any smart device now or in ten years.
This is also the moment to check the box fill, because smart switches are physically deeper than the toggle they replace and a crowded box is a real constraint.
Solution two: no-neutral smart switches
Some devices trickle a tiny current through the load to power themselves. They work well with incandescent loads and are hit and miss with LEDs, which can glow faintly or flicker because that trickle is enough to partially light them.
A bypass capacitor at the fixture usually solves the glow. It is a legitimate option, just one with more variables than running a neutral.
Solution three: move the smarts to the fixture
Smart bulbs, or an in-line module installed at the fixture where the neutral already is, keep the wall switch mechanical. The catch is that the switch must stay on for the smart control to work, which is a household training problem more than a technical one.
Smart switches paired with in-line modules solve that, giving you a wall control that behaves normally and a smart system that stays reachable.
Plan for three-ways before you start
Three-way and four-way circuits are where DIY smart switch projects usually fail. Each ecosystem handles them differently, some needing a companion switch, others needing a full rewire of the travellers. Work out the approach before buying twelve switches.