Smart switches when you have no neutral wire

An ordinary switch is a gap in a wire. It needs no power of its own, so a single cable to the box is enough: hot in, switched hot out. A smart switch is a small computer with a radio, and it has to stay powered even when the light is off.

With a neutral, the switch has a proper return path and draws its power cleanly. Without one, it has to trickle a small current through the bulb itself. Lutron describes the two jobs the neutral does: it gives the dimmer a zero-cross reference, and it acts as a drain for excess voltage rather than leaking it to the load. Lutron also names the symptom when that leak has nowhere to go - LEDs react by not fully turning off.

This is why houses built before smart switches existed are the ones with the problem, and why the answer is never just buy a different brand.

1. A switch designed for two wires. Lutron's Caseta PD-6WCL is described on its own spec sheet as a two-wire dimmer, no neutral required, rated up to 150W of LED. It publishes what it needs instead: a minimum load of 25W incandescent or one LED bulb, up to 17 bulbs, and a wall box at least 2 1/4 inches deep. Aqara's no-neutral switch takes the same approach on Zigbee, with 200W per way of LED and a required hub.

2. A bypass at the fixture. Where a no-neutral switch flickers or ghosts on a small LED load, the fix is a capacitor at the light rather than a different switch. Lutron's LUT-MLC instruction sheet describes it as being for switches controlling CFL, LED and fluorescent lighting without a neutral connection available, and says only one is required per switch. Inovelli publishes the same idea as a bypass for its Blue Series.

3. Skip the switch entirely. Smart bulbs need no neutral because they are powered by the socket. Leave the wall switch on, control the bulbs, and put a battery remote like the Lutron Aurora over the switch so nobody kills the power by habit. For a rental this is usually the only sanctioned route - the wiring stays untouched.

Lutron Caseta dimmer - the default recommendation. It is the best-documented no-neutral device in the category: a published spec sheet, a published minimum load, a published box depth, and a bypass product from the same manufacturer if the LEDs misbehave. It also dims, which the Aqara does not.
Cons: it needs a Lutron hub for app and voice control; the no-neutral claim applies to specific models, not the whole Caseta range.

Aqara no-neutral switch - for a Zigbee or HomeKit house. 200W per way of LED is more headroom than most rooms need, and it works with Apple Home, Google, Alexa and SmartThings through an Aqara hub.
Cons: the hub is not optional; it is single-pole only, so no 3-way; it switches rather than dims; and Aqara's spec sheet publishes no minimum load, only the retail listing's 3W.

Lutron Aurora - the no-wiring answer. It clamps over a standard toggle switch, holds it on, and gives you a dimmer for Philips Hue bulbs underneath. No box, no neutral, no screws into the wiring.
Cons: it only controls Hue bulbs, so the lighting cost moves to the bulbs; and it covers the switch, which some people dislike.

Confirm the box, not the house. Wiring varies room to room in the same building. The switch by the front door may have a neutral while the hall switch does not.

Check the model, not the brand. Leviton's DN series is designed for retrofit where there is no neutral, while its Decora Smart Wi-Fi products require one. Lutron's own range splits the same way. A brand is never an answer here; a model number is.

Budget for a bypass on small loads. If the fixture holds one LED bulb, plan on a capacitor at the fixture from the start rather than diagnosing a flicker later.

If you rent, do not open the box. Smart bulbs plus a remote get you nearly all of the function with none of the wiring - the renter version is in renter-friendly smart lighting.