Smartmedia was the first consumer flash memory format, going back to at least 1997, and probably a little earlier. I'm not counting "linear flash nonsense that 19 early-adopter businessmen owned" here - Smartmedia was the first card you could walk into a Circuit City and buy for use in a piece of cheap plastic crap purchased at that same Circuit City for under $200.
As a result, there's a good chance you, would-be retroelectronics historian who has found my website, need to know what quirks it has that are relevant to your needs in the 21st century. I will help.
SmartMedia is so old that it didn't even start out with a flashy, trademarkable name. It was initially called SSFDC, for Solid State Floppy Disk Card. Boy howdy, you couldn't come up with a more Japanese term if you tried.
Keep this term in mind - if you're delving the depths of mid-90s consumer goods, it will occasionally come up and you will need to know that it's the same thing as SmartMedia. I prefer SSFDC, because "SM" seems like a terrible abbreviation for reasons I can't explain.
Find above a picture of the front and back of a collection of SSFDCs. They are in roughly chronological order, as far as I know.
There is no way to know which way to insert an SSFDC card. Every device differs, there is no keying mechanism (that I've ever seen) and no obvious indications. You just need to try it both ways. If it doesn't work, flip it over (you won't hurt it.) If it won't go in, push harder; the slots are primitive and often tighter than they should be.
SmartMedia cards are the thinnest flash cards in existence. I think they're thinner than micro-SD but don't quote me on that. They feel incredibly fragile, and while I'm not 100% sure how they're constructed, I accidentally bent one recently and the gold contact patch popped off the surface.
It remained partially attached, and kept working. This either means that the memory chip is attached to the bottom of the contact patch and the rest of the card is nothing more than a handle, or it means that there are flexible leads between the contacts and the chip, or that I ripped off part of the contact array but not all of it. I don't know which it is, so don't risk it; avoid bending these.
The very late (32MB-128MB) cards have a distinct patch on the backside that seems to suggest the chip is mounted on a separate substrate from the rest of the card body.
SSFDC cards come in two voltages. In the picture above, notice the leftmost card says -5, indicating it's the earlier 5-volt type. The other devices are labeled 3.3V and 3V; both are the same and will work in the same devices, I don't know why they're labeled differently.
As far as I can tell, only the earliest cards were 5V. Even by 1997, devices were switching to 3.3V, and that's what you'll mostly find, but you'll want to have both voltages on hand. Most devices made after 3.3 was introduced will be labeled as such; anything not labeled is probably 5V. It's harmless to experiment, so try both.
The voltage is keyed into the card. When looking at the front of the card with the contacts facing up, 5 volt cards will have the upper left corner cut, and 3.3 volt cards will have the upper right corner cut.
At one point, the keyed corner was supposed to be used by readers to prevent reverse insertion. To date, I have not encountered a device that does this. Either nobody bothered to build in the mechanism, or the card is so thin that it just slips over it, or they gave up when the second voltage hit the market and rendered the key ambiguous. I'm not sure which, but just don't assume that because you could insert a card, that you did it right. See above; if it doesn't work, flip it over.
In my experience, voltage is the only important factor. I haven't found a 3.3V device that wouldn't read, say, a 128MB card. There could be exceptions.
It's slow as molasses. Expect this. You will not find a USB 2.0 card reader; there's no point, and SSFDC was dead by then.
Most readers are limited to one voltage or another; this is never labeled or described in the manual, in my experience. Below, I've listed pictures and model numbers for readers I've tried, some of which have special, useful features.
The majority of readers I've found are USB 1.1, and are not USB Mass Storage Class devices. This means they will not "just work" on a modern OS. You need a driver, and you will not find one that works on any OS past Windows 2000 / MacOS 9. To find drivers for these, you will almost certainly need to dredge up the manufacturer's site on Internet Archive. This can be a challenge, since some devices were sold off to other companies, and you need to figure out who owned them originally. Google Books can be helpful.
I have found one exception, a reader which shows up as a generic mass storage device, described below. If you know of others, email me (articles@gekk.info,) ideally with a photo, and I'll try to add it here.
The above device works on any OS with USB support. It's a combo SSFDC/CF reader labeled Memorex 5395-5425. This can probably be found with many other brand names on it, but I don't know them. It is limited to 3.3V cards.
The above device, a Sandisk Imagemate SDDR-09, is special because it reads both 3.3V and 5V cards. Very few readers do. It is not a mass storage devices; it requires a special driver. The Windows 9x version is here: sddr09-200.exe. I got it from an old Sandisk page containing drivers for other contemporary SanDisk readers, via Internet Archive. You can do the same here: Sandisk website.
For completeness, here is a Zio! reader that I struggled to get working. The only model number is on the internal chip, but you can see it since the case is translucent: EUSB-02. This reader requires a driver, which I've lost. It can only do 5V.