SteamWorld Dig 2

You will trigger an alarm when you come too close to a robot with a blue ghost hovering around it. When that happens, the ghost will enter the robot and activate it along with all the robots in the vicinity. Don't worry, you will most certainly notice when you trigger an alarm.

Although the achievement allows for triggering two alarms, you don't have any leeway. You can't make your way through Vectron without triggering two alarms. In both cases, a robot will block your way and the only way to move past him will be to trigger the alarm. First such occurrence is the very first robot with a ghost which you will encounter. The second one is the last one before leaving Vectron.

If you accidentally trigger the alarm by activating some other robot, you can allow the activated robots to kill you. This will reset your position to the beginning of the current area (not the whole Vectron) but it will also mean that the alarm you have just triggered will not count. This means that you will still be able to get the achievement if you don't trigger the alarm on your next try. You can repeat a section until you get it right.