Eyefi is a technology that's been around for a while, that combines a regular SD memory card with a wireless chipset so that images that are being recorded onto the card by the camera can be transmitted wirelessly to another device. The cards can be purchased mainly on Amazon. The technology has also been licensed to Toshiba for their FlashAir series. Compared to Eyefi, the FlashAir cards have a somewhat lower range and less sophistication but can still be used for the same overall purpose. Both systems have a range measured in the tens of metres in any case, they don't have a big antenna or high power output, they are really just useful for transferring pictures between two devices that it would be hard to connect with a cable. This is especially applicable to the Nexus 5X since it doesn't have an SD card slot, and just about any phone with a MicroUSB socket can't be connected to another device like a camera with a regular USB cable - a special host adapter and cables would be required. (This technology is called USB OTG, and is not supported by all phones, however the Nexus 5X does support it, but at the moment I am not planning to experiment with it.)
My interest has shifted to the EyeFi technology since I stopped using the Ixus 135 camera that I bought a few years ago, which has built in Wifi that works through a mobile phone app that Canon provide to automatically transfer images. The Ixus 135 is a much less sophisticated camera than the Powershot SX260 that I currently use, but the SX260 doesn't have Wifi. So to get this capability, if I don't want to buy a new camera and don't want to go back to using the Ixus 135 then I have to look at one of these cards. The reason I want to use the SX260 is for superior low light performance or optical zoom etc which a camera phone can't really manage. Being able to transfer photos wirelessly to the phone in real time means I don't have to download them to a computer and then transfer them to the phone by Bluetooth or Google Drive.
The Toshiba card costs about $40-50 depending on the model so I will have a look at buying one when I have time.
