Neuro-depolarizing device
From Memory Alpha, the free Star Trek reference.
A neuro-depolarizing device is a suicide mechanism used by covert operatives to prevent others from extracting information from their mind. It is apparently implanted in the operatives body and can be activated while the operative is restrained in a force field. The device prevents the use of Romulan mind probes.
In 2375, Luther Sloan of Section 31 activated a neuro-depolarizing device in an attempt to prevent Doctor Julian Bashir from obtaining a cure for the morphogenic virus designed by Section 31. (DS9: "Extreme Measures")
