Megapol Stun Grenade
Used and marketed by Megapol as an effective non-lethal weapon, the Stun Grenade provides X-COM with a way to capture live aliens for vital research. The gas that the grenade releases will stun any persons who remain in the cloud too long. Aliens caught in the cloud will attempt to escape before being stunned. The gas is not affected by Personal Disruptor Shields, so stun grenades may be the best way to capture shielded aliens.
To arm, left-click on the grenade and set the time delay. Note, however, that the timer begins as soon as the grenade leaves the agent’s hand: on the shortest fuse, the grenade explodes in his face! Also note that the timer cannot be stopped after throwing/dropping, even if an agent picks up the grenade. To detonate the grenade on impact, right-click on it and throw.
"The Stun Grenade can be used to stun targets within a small area for a brief time. Larger Aliens may need weakening before they can be stunned."