Reaction fire triggers

Certain actions will trigger reaction fire from aliens; others will not, even though they may reduce your TUs. The following is a (presently incomplete) list of which actions will and will not trigger reaction fire. Opposing units also need to be facing your unit(s) and have sufficient TUs available; see Reaction fire formula for more details.

Will trigger reaction shots:

• Firing a weapon
• Kneeling
• Any walking/flying movement (including opening a door)
• Hitting an alien not facing you (they will spin around and return fire)
• Throwing any object
• Using a Stun Rod

Will never trigger reaction shots:

• Turning in place
• Firing a weapon from beyond the alien's visual range
• Firing a weapon from a position hidden to the alien
• Priming a grenade
• Firing at (but missing) an alien not facing you
• Any action on the inventory screen
• Using a Medi-Kit, Mind Probe or Motion Scanner

Currently unknown/untested:

• Using a lift