The Stun Mine is a gadget that Daud can acquire in The Knife of Dunwall. These mines can either be purchased, or found in any of the three missions.
Function
The stun mine acts in a very similar manner to the Arc Mine in The Knife of Dunwall. The difference, however, is that the stun mine expels a bolt of electricity--enough to instantly render those in its proximity unconscious, rather than turning them into ash, like the arc mine. The intended use for this gadget is for non-lethal traps and takedowns.
Upgrades
Daud can acquire two upgrades for the stun mine: A capacity upgrade to carry six mines instead of three, and an upgrade that gives the stun mine an extra charge to render more than one target unconscious (The arc mine can also be upgraded with these options).