University of California San Diego nanoengineers developed a flexible, wearable sensor that measures the blood alcohol level of its wearer and transmits the info to a mobile device. From UCSD News:
The device consists of a temporary tattoo—which sticks to the skin, induces sweat and electrochemically detects the alcohol level—and a portable flexible electronic circuit board, which is connected to the tattoo by a magnet and can communicate the information to a mobile device via Bluetooth.
The device could be integrated with a car's alcohol ignition interlocks, or friends could use it to check up on each other before handing over the car keys, he added.
"When you're out at a party or at a bar, this sensor could send alerts to your phone to let you know how much you've been drinking," said Jayoung Kim, a materials science and engineering PhD student.