The device, from a startup called Thync, consists of a set of electrodes connected to a smartphone.
It has a short-lived energising effect that feels a little like drinking a can of Red Bull, according to its makers.
Thync cofounder Jamie Tyler, a professor at Arizona State University, said the device can also be used to produce a calming effect.
Marom Bikson, a professor of biomedical engineering at City College of New York, has used a prototype of Thync's device in a 100-person study (funded by the company) that focused on its calming effects.
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"For some people - not everyone - the effect is really profound. Within minutes, they're feeling significantly different in a way that is as powerful as anything else I could imagine short of a narcotic," Bikson added.
The device uses a form of transcranial direct current stimulation (TDCS). The device applies a barely perceptible electrical current to the skin on the head at different places for the relaxing effect.
Most TDCS research focuses on trying to use the electrical current to directly affect the outer part of the brain.
Tyler is also developing technology that uses ultrasound to affect the brain directly without surgery or drugs.
"The ultrasound work might lead to treatments for psychiatric disorders and offer new insights into how the brain works," said Amit Etkin, a professor of psychiatry and behavioural science at Stanford.
He's starting a partnership with Tyler that will investigate how the technology might help treat depression, post-traumatic stress disorder, and the tremors associated with Parkinson's.