Way back in 1E, lower level wizards in our game rarely consumed a coveted spell slot
with detect magic when they were out adventuring. With so few slots available, you loaded up on reliable party saving spells, or escape spells. That means when gathering loot, you grabbed everything you could that might even remotely have the chance of being magical and sorted it all at in the safe confines of whatever you called safe confines. There, without the constant threat of annihilation you felt marginally safe using up spell slot on detect magic and hoped for the euphoric moment of discovering the party had indeed grabbed the right stuff.
With the addition of cantrips in 3E, detect magic could safely be used in the field. Of course there were the complications as everything in 3E had complications. You needed to build your spellcraft skill to keep a high success rate. However, if you took a few rounds you would learn not just whether there were magic items, but how many, where, how strong and what school. If you wanted to hide you magic items there was still the old stand by various thicknesses of various materials but barring that, you pretty much found all the magic items if you cast the spell.
I never gave the changes between 1E and 3E too much thought until I saw the 5E detect magic spell in use.
For the duration, you sense the presence of magic within 30 feet of you.
I take this as you just 'sense' that magic is within 30' of you in any direction. You would not know the direction, just sense the existence/presence of magic within 30'. You would not know the number of items, or even the relative strength.
If you sense magic in this way, you can use your action to see a faint aura around any visible creature or object in the area that bears magic, and you learn its school of magic, if any.
Key word here is visible. If you do not see it, you would not see the aura. I like this so much. You would still have to search for the magic item which you sensed. This brings the other players back into the game. Sure, you might find clever ways of narrowing the search area using some geometry and such. But just having the item obscured by a floor board, a closed cabinet, a locked draw, you name it - keeps the search in 'searching for treasure'.
The spell can penetrate most barriers, but it is blocked by 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood or dirt.
This section refers back to the sense statement. If there is a visible barrier of this sort, you certainly could not see the item anyway. I like that they remain consistent with earlier editions in this way.
Low level 1E kept the search in by simply making spells rare. I like that detect magic can be cast as a ritual, and like even more that simple change in language which keeps the search in the game. It definitely gets my DM juices flowing with ideas.
One interesting point, as I tried to look up the school of magic for the potion they located, I did not find one. Not sure if I am supposed to extrapolate that, or, as implied by the spell (if any) not every item/object will have a school. Until I learn otherwise, I am going with the later.
The dice never lie.
