D&D 5E How do you do secret doors?

[MNblockhead]

I roll a d20 against the party's passive perception, using a modifier equal to the DC of the door -9. If it beats everyone's Passive Perception, then it's not seen. If someone is actively searching, I allow either a Perception or Investigation (player's choice) instead. Once found, an Investigation check is required to figure out how to open it.

[MENTION=6775477]Shiroiken[/MENTION], curious why you use "-9" ? -10 seems more in keeping with 5e (unless I'm missing something).

How do you handle advantage on Perception? RAW is to apply +5 to passive score but I could also see handling it as 2 rolls and taking the lower (since trying to roll under instead of over).

 

[Shiroiken]

I remember it had to do with the flip of the DC, but I don't recall the exact math at the moment. Using -10 would be simpler, but the odds would be different, favoring the passive score.

As for Advantage, I give the door Disadvantage instead. If there is some reason the door would also have Disadvantage, then the PC gains +5 in addition (making it very likely the passive score will succeed).