Finding neutral wire in wall boxes

Question

I'm trying to replace four switches in a 4-gang box. All four are on different circuits.

From left to right:

• This is a 3 way switch and I want to replace it with another 3-way switch. I think I know how to do this one.
• This is a 3 way switch which I want to replace with a "smart" 3-way switch that requires a neutral wire.
• This is a single-pole switch that I want to replace with a "smart" switch. I'm planning to use the same model as for the other one (it supports 3-way, but also single-pole applications).
• This is a 4-way switch. I've already swapped it out.

There are two pairs of white wires connected (the white caps at the top and bottom). The top pair seems to go to the same place as the two black wires from the single-pole switch. The top one seems to go between the input and output of the four-way switch.

My questions are: which of the two middle switches is it possible to replace with these smart switches? (If not, I have regular single-pole and 3-way switches I'll use instead, and maybe use smart bulbs instead, but they are for outdoor sconces, and I'd rather have a single smart switch rather than needing to use smart bulbs). More generally, what is the best way to identify a neutral wire in this scenario?

If it matters, this is in Indiana, in a house built in the mid 1990s. Also, I've changed a bunch of switches so far, and basically none of them have had the ground connected to the switch itself. I think they're all tied together in the back of this box.

EDIT: This is a view of the box with the corresponding 3-way to the one without a neutral (it's in the garage). The switch on the right (black and white wires running to the bottom right, out of frame) is a single-pole, unrelated to this issue.

The one on the left is the one I'm interested in. It seems like there are the black and white wires coming out of the bottom (on the left) into the wire connectors, then the white goes out along with the red, white, and black from the switch.

So, assuming the white one there is neutral. I can put the smart switch in the garage, and a companion switch where the original one was (and change the wires there to just be a passthrough).

Answer 1

You don't appear to have a possible neutral available here for anything but the single pole and the 4-way, so the 3-way is not an option for a smart switch requiring a neutral if they are all on different circuits.

The whites on the 3-ways are Travelers, not Neutrals.

We can strongly suspect that the white on the single pole is a neutral because it comes in the same cable with the presumed always-hot and goes out the cable with the presumed switched hot. Similar for the 4-way, though there it's paired with two switched hots at this segment.

We know that the whites on the 3-ways are travelers because they are connected to the switch terminals, and also because the 3-ways are "dead-ended" here - they only connect to the one cable each.

You may be able to retrofit a "smart" setup by replacing both switches on that circuit/lamp with one being a switch that actually switches, and the other being a satellite switch that sends it a signal to switch, and repurposing the white in the cable in between them as a neutral to power the satellite switch.