Smartphone cameras have gotten pretty good, but sometimes you want something with a bit more power. You could carry around a DSLR, of course, but DxO's One accessory camera might get the job done — and in a much smaller package. The One is a self-contained camera that snaps onto your iPhone and has a 20-megapixel, 1-inch sensor — much larger than what you'd find in any phone, although some have similar pixel counts.
The One uses your iPhone as its (rotatable) LCD screen, letting you fiddle with settings or review shots, though the guts of the camera are in the One itself, as is the shutter button and bright F/1.8 lens. There's even a slot for a Micro SD card, so you don't take up all your phone's storage space with the big RAW images the One can shoot.
And if you're trying to be inconspicuous, you can use the One on its own — with no LCD, just like the old days. Point at your target, hit the button and hope it turns out!
At $600, the DxO One isn't a cheap accessory, but it might just be the right thing to take on a vacation, or to carry around in a purse instead of a bulky DSLR.