Then there’s @Pogue’s Latest Law: “The more convenient a device is, the worse the audio/visual quality.”

Take the iPod, for example. Millions buy it for its convenience, despite the fact that the music files’ audio quality is usually far lower than what they would hear on a CD.

Similarly, hundreds of millions of people now take most of their photos with cellphone cameras, even though the picture quality is far worse than a real camera’s. There’s no zoom, no real flash, low resolution. You can’t photograph action without blurriness, you can’t get that soft-background look, and cameraphones are worthless in low light.

But we put up with those drawbacks, because cellphones are incredibly convenient. You always have yours with you — and, even better, you can transmit a picture or movie right from the phone. Send it to another phone, to an e-mail address, to a Web site or blog, on the spot, without even stopping at home first. That’s powerful stuff.

Nice choice, huh? You can take nice pictures that remain landlocked on the camera, or lousy ones to upload or send.

Now there’s a product that bridges that gap. You can take photos with your favorite camera, but transmit or upload them to the world from your cellphone, on the spot. It’s a memory card, of all things: The Eye-Fi Mobile X2 card ($80).

Eye-Fi cards have been around for a while. The first ones did one thing very well: they transferred photos from your camera to your computer — and online sites like Flickr or Picasa — when you’re in a Wi-Fi hot spot. (Yes, that’s right: the Eye-Fi folks have squeezed Wi-Fi circuitry onto a memory card the size of your thumbnail. Think about that too hard, and you’ll give yourself a headache.)

Eventually, the company took this feature to its logical conclusion: the bottomless memory card. If you’re in Wi-Fi, you can keep snapping photos. The card steadily backs them up to your computer or a Web site, and then deletes the backed-up photos from the card to make room for new ones. You never run out of card space.

Recent models have added geotagging (your geographical coordinates get invisibly stamped onto each photo, so you can view them later on a map online) and the ability to transfer photos in RAW format. All the cards are physically identical, though; you can buy a card intended for one purpose (like the Mobile X2), and then pay $30 each to add features from other cards. (If this all seems confusing, you’re right.)

But the Mobile X2 is the first Eye-Fi card that can perform its magic even when you’re not in a Wi-Fi hot spot.

After some setup, you put this 8-gigabyte card into your camera. (It’s an SD card, so it fits almost every camera on earth.) From now on, every time you take a photo or record a video, it gets transmitted wirelessly to your iPhone, iPad or Android phone — at full, beautiful quality and resolution. Once it’s there, you can e-mail it, text-message it, post it to Flickr or another Web site, and otherwise manipulate it exactly as though it had been born on that phone or tablet.

A photo takes 5 to 30 seconds to transfer, depending on the size of the photo file. (A video can take far longer.)

In essence, the Mobile X2 card turns any camera, from a cheap point-and-shoot to an expensive digital S.L.R., into a wireless camera. (I met one photographer who is using this card in his portrait studio. He has the card set up to fling each photo onto his iPad, so he can inspect his work on a much bigger, better screen than on his camera. It’s a pretty amazing setup.)

There are two bits of not-so-fine print, though, that you should consider before you shell out the $80.

E-mail: pogue@nytimes.com

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