Phone “silent” switch is completely ignored by many applications

Was recently in a very important work situation so I had to make sure my iPhone was completely silent. I manually lowered all the volume then set it to silent mode through the "switch" then AirPlane mode to help quell my fears then to finish the procedure, I manually checked and verified that indeed, no sound would play given an arbitrary source within the phone (for example an application).Needless to say, my worst fears came to fruition and shocked me, as I was confident it was not possible. The cause of the sound was through Bluetooth, a device disconnected causing the internal speakers on the iPhone to play, full volume oddly enough. This is very frustrating, is there a way that effectively prevents any and all sound ? Im aware of the Do Not Disturb option but im afraid that will scale the risk by some integer k as the feature allows different settings for every 'instance' that can lead to sound effectively turning this from a $o(n)$ scenario into $o(n!)$.