I picked up a Tilt Digital Hydrometer
several weeks ago, and have been evaluating it.
The Tilt is a BluetoothLE device that uses an accelerometer in order to determine the SG of a liquid. The Tilt is weighted such that it tilts at a pre-defined angle in water. The accelerometer measures this tilt, and converts it into an SG reading which is broadcast every 10 seconds or so via iBeacon advertisement. There are Android and iOS apps that read and display these readings. A digital thermometer is also present in the Tilt, and a temp reading is also broadcast with the SG.
You use the Tilt by sanitizing it, and dropping it directly into your carboy/brew bucket/conical/whatever and placing your Android/iOS device nearby. The apps have the ability to send the data into the cloud
I didn't have any BluetoothLE-enabled devices with which to take readings, so I set about configuring a RaspberryPi 3 to read, save and display the results. Here is the latest test with an IPA I helped a friend make:
It seems to work pretty well, but a $200 a pop, it may be beyond the means of many homebrewers.