Aliens Colonial Marines
60 Achievements
1,250
35-40h
No Need For Alarm
Complete One Bullet without setting off the alarm
20
How to unlock the No Need For Alarm achievement in Aliens Colonial Marines - Definitive Guide
The first thing to do after the scene with Bella is run up the stairs. The scientist will see you through the window so you have to run to the control panel on the wall by the door. As you go along you can scout ahead to see the situation and use your motion tracker. I used a suppressor on my pulse rifle and went for headshots as well. Reload at any time you screw up. Do not worry about the outside portion with the APC but when you get back inside to shut off the 3 power cores be stealthy again just to be safe. After taking out the cores and going back upstairs to shut the power off, the achievement will pop.
The first thing to do after the scene with Bella is run up the stairs. The scientist will see you through the window so you have to run to the control panel on the wall by the door. As you go along you can scout ahead to see the situation and use your motion tracker. I used a suppressor on my pulse rifle and went for headshots as well. Reload at any time you screw up. Do not worry about the outside portion with the APC but when you get back inside to shut off the 3 power cores be stealthy again just to be safe. After taking out the cores and going back upstairs to shut the power off, the achievement will pop.
You need to get through the labs without setting off an alarm in mission 7 (One Bullet). The very first scientist will spot you and set off an alarm. This is inevitable, but won't influence the achievement. Speed (and shotgun for close quarters) is your best friend for this. Each time you open a door, you must quickly kill everyone in the room before they hit an alarm (located on a wall). If they spot you everything is fine, they are just not allowed to use the alarm switch. Rush in with a shotgun on Recruit difficulty and kill them quickly. If they reach an alarm, it will begin a countdown. If you hit the switch () to cancel the countdown, the achievement will still unlock. If you're sure you've set off an alarm, pause and select "restart checkpoint" to try again. The achievement pops when you've completed the mission.
Video Guide by AuraSolier313:
This trophy can only be earned in the seventh chapter, One Bullet.
Once you reach the facility, you will have to make your way through various labs with scientists in them. Along the way you will hear the scientists say "sound the alarm", after which they will make a run for an alarm button to signal reinforcements. You simply need to kill them before the alarm is set off. Although this trophy sounds difficult, it's actually a lot easier than you may think. There are only two rooms containing alarm buttons and even if the button is pressed, there is a 10 second delay before the alarm actually goes off. If a scientist presses a button, you will hear an announcement over the intercom, after which you will have 10 seconds to deactivate it by pressing on the button. The rooms only contain three scientists at most and they all go down relatively quickly so this shouldn’t be too difficult to earn, even on Ultimate Badass difficulty.
Please note that the trophy unlocks at the END of the mission, so you will need to finish it entirely once you meet the requirements in the labs.