Most military and major organisations have their buildings and bases fitted with alarm systems. When a guard spots an unauthorized agent, they may run to the nearest alarm switch and alert allies of the situation. The presence of such security severely bolsters the need for either stealth, or speed.

In-Game

Alarm systems appear in numerous levels in Perfect Dark. When triggered, the alarm will do one of two things: send guards, or fail the mission.

Once the alarm sounds, any objectives refraining you from not doing so in the first place will fail and enemies will start to swarm in. It's nearly impossible to evade alerted personnel, so direct combat is necessary.

Triggers

Alarms can be sounded in different ways:

• Security cameras.
• Traditional alarm switches.
• Computer terminals linked directly to the system.
• By Radioing HQ/Base of the situation.
• Unauthorized electronic access to high-level security systems (Vaults etc.)
• Large explosions.

Tactics

• Guards will always shout out that they will sound the alarm.
• If the guard going for the alarm is eliminated while other guards are around, one will automatically stop what he is doing to try and trigger it himself.
• Destroying the alarm switches may be helpful, but bear in mind that most will be invincible.
• FBI Agents do not need alarm panels, but radio into their fist for a few seconds after spotting the player.

Appearances

Note alarms that will fail its appropriate mission are marked with an asterisk (*) unless noted otherwise

DataDyne Central: Defection

• Alarms are sounded when Jo gets spotted by security cameras (SA/PA)
• If you allow Cassandra to reach her desk, she will call security

DataDyne Research: Investigation

• Each scientist has a monitor that will trigger the alarm (SA/PA)
• If allowed, the third scientist you encounter will always run for his alarm panel  (SP/PA) 

Chicago: Stealth

• All FBI Agents will radio HQ if they spot you*

G5 Building: Reconnaissance

• Guards on the first floor will consistently rush for an alarm panel if they spot you*
• Hacking the safe triggers the alarm*
  • Unless after you have successfully recorded the meeting, then the mission will not fail.
• Prematurely detonating the Remote Mine will also trigger the alarm*
  • Detonating the Remote Mine at the end will retrigger the alarm but won't fail the mission.

Air Base: Espionage

• The guards outside will go for an alarm panel until you eliminate them or gain the Disguise*
• Going into the Airbase, without a disguise, will trigger the alarm*
• Harming the woman in the lobby or any guards in her sight will force her to sound the alarm*
• Failure to check in your weapons in time will trigger the alarm*
• Failure to deactivate the security system while your suitcase is being processed will trigger the alarm*

Pelagic II: Exploration

• This level is littered with alarm panels along with guards that are very eager to trigger them.

Mr. Blonde's Revenge

• If Cassandra's guards see you, they will rush for the elevator and sound the alarm (A)
  • If Cassandra's guards see you, they will rush for the elevator and sound the alarm (SA/PA)*

Maian SOS

• Nearly halfway into the level, the alarm will automatically sound. This alarm is just fan audio effect, though.

Quotes

You'll need to act swiftly when guards say either of these quotes:

• Activate the Alarm!
• Warn the others...!

FBI Agents have their own quotes:

• Base, we have an intruder!...
• We have a Code Blue situation...