In this edition matrix perception work similar to regular perception.
If there are two ninjas hiding in the shadows you take a regular perception test and depending on how many hits you got (and depending on how well they are hidden) you might notice both of them, just one of them or none none of them.
If there are two hidden hackers in a host the spider take a matrix perception test and depending on how many hits he got (and depending on how well the hackers are hidden) he might notice both of them, just one of them or none none of them.
If one of the ninjas is under the influence of Concealment then he would not been spotted in this case.
If one of the hackers is under the influence of Phantom then he would not been spotted in this case.
If a hidden sniper take a shot at you then you are now "aware" of the sniper and you can take a regular perception test to spot this specific sniper.
If a hidden hacker is attacking you with a data spike you are now "aware" of the hacker and you can take a matrix perception test to spot the specific hacker.
If the sniper is under the influence of Concealment critter power then you still have a chance to spot the sniper, but your perception test still need to overcome the Concealment power.
If the hacker is under the influence of Phantom sprite power then you will still have a chance to spot the hacker, but your perception test still need to overcome the Phantom power.
If you spot a guard you typically also spot that he is wielding an weapon.
If you spot a silent running PAN then you also spot all the devices that are part of the PAN.
If the guards weapon is under the influence of the Concealment power then you will typically not see it.
If the target's weapon is under the influence of Phantom then you will typically not see it's device icon.
If you specifically look for the weapon then you are allowed to take a Perception test, but your perception test still need to overcome the Concealment power.
If specifically look for the weapon's device icon (perhaps you or someone in the team see that the guard have a weapon) then you are allowed to take a Matrix Perception test, but your matrix perception test will need to overcome the Phantom power (and if you fail you might probably think that it was just wireless disabled to begin with).