Magnetic coercion device

the Transcranial Magnetic Stimulator is an apparatus that stimulates the brain through the skull with electromagnetic fields. Search Wikipedia for "god helmet". It's less precise than sticking electrodes directly into the brain but much easier to do.

If you stimulate the right areas of the brain the right way you can get a variety of effects. From flashes of light to visions of God to turning off aggression (actually done in a famous experiment with a bull).

Now if you figure out which parts of the brain to stimulate and you can make a device thats accurate enough (you might need to integrate this into an MRI machine), you can cause cause such useful effects as lowering inhibition (the principle behind so called truth serums) or increasing trust. Now this would be useful in Interrogating prisoners.