Electronic tattoos? You bet. Turns out they may be very exciting and could make electronic telepathy possible. Temporary electronic tattoos, as they are called, are about as thick as the average diameter of a human hair (e.g., 100 microns). They involve circuitry that is embedded in a rubbery polyester that allows them to bend and stretch. Think of electronic tattoos as foldable, stretchable electrode arrays that can non-invasively measure neural (EEG) signals without the need for any type of gel. When placed on the skin, these tattoos are barely visible, but they can detect electrical signals linked with brain waves and incorporate solar cells for power and antennas that allow them to communicate wirelessly, and can contain thermal sensors to monitor skin temperature along with light detectors to analyze blood oxygen levels. Researchers at UC, San Diego, are working on optimizing the placement of the electrodes to pick up more complex brainwaves. This could help monitor fetal heart rates during pregnancy or depression and Alzheimer's disease in adults, each of which have characteristic patterns of neural activity. The research team is also working to modify the tattoo to transmit data wirelessly to a smartphone. Eventually, scientists hope the device could identify other complex patterns of brain activity, such as those that might be used to control a prosthetic limb.