TL;DR Check with your DM
You never "take" a passive Perception check. If your DM is using the guidelines from the basic rules, whenever you have a chance to detect a hidden object, like a secret door or loose floor tiles over a pressure plate, or a hiding enemy, the DM should be comparing the PC's passive Perception to the search DC (Stealth check for creatures) of anything you may notice. If you are actively searching, the DM should be comparing the results of your roll. A lot of people state the passive check is a floor for the active check, but in reality, you should never be making an active check for something you already have discovered, so it would never actually come into play, unless your DM forgot to check.
A passive check is a special kind of ability check that doesn't involve any die rolls. Such a check can represent the average result for a task done repeatedly, such as searching for secret doors over and over again, or can be used when the DM wants to secretly determine whether the characters succeed at something without rolling dice, such as noticing a hidden monster.
A trap's description specifies the checks and DCs needed to detect it, disable it, or both. A character actively looking for a trap can attempt a Wisdom (Perception) check against the trap's DC. You can also compare the DC to detect the trap with each character's passive Wisdom (Perception) score to determine whether anyone in the party notices the trap in passing.
The DM determines who might be surprised. If neither side tries to be stealthy, they automatically notice each other. Otherwise, the DM compares the Dexterity (Stealth) checks of anyone hiding with the passive Wisdom (Perception) score of each creature on the opposing side. Any character or monster that doesn't notice a threat is surprised at the start of the encounter.
It's important to note, there's a lot of the DM can language as well as, from the DMG's introduction,
The D&D rules help you and the other players have a good time, but the rules aren’t in charge. You’re the DM, and you are in charge of the game.
So, your milage may vary, that is, in general, check with your DM.
Since you are the DM
In your case, you are the DM, so you get to decide. What works for me is, I always compare passive Perception before I describe the scene, so that information is included when I lay out the description. If a player wants to then actively search, then I ask for the appropriate roll, or simply offer the information, if the player's choice is self evident.
For example, if there's a key in the dresser drawer under some clothes and the player says
I search the dresser
and I say,
It's filled with folded shirts and garments
and the player says,
I pick them up and look under them
You find a key.
No rolls, just role play.