Detect Magic as a sense

[PhoenixPhyre]

I'm considering doing the following:

1. (General rule, available to everyone). All creatures can sense the following events within 30 feet of them, as long as there is a clear path to the source. This is a binary sense (yes/no/present/absent) and does not give any targeting information or other information.
1a. A spell of 1st level or higher being cast. Subtle spell counters this.
1b. A major magical effect, such as that of an active Very Rare or rarer magical item or an ongoing, free-standing spell effect of 5th level or higher. Note that spell effects anchored in a person (ie spells active on a person) do not count for this.
1c. Substantial environmental magic, such as being in the vicinity of the lair of a legendary creature.

2. (For all PCs and monsters of CR or level 11+ and anyone capable of casting 3rd level or higher spells). The range extends to 60 feet and you can now detect cantrips and free-standing spells of 3rd level (or Uncommon items). For spells being cast, you know who is casting them if you can see the caster[1]. Otherwise you simply know a spell is being cast.

3. (For all PCs and monsters of CR or level 17+ and anyone capable of casting 6th level or higher spells). You have the passive effect of detect magic (ie getting the "ping") as a passive sense.

4. The warlock invocation removes concentration from detect magic.

5. Detect magic also gives you a sense of the intent of the magic[2] and you automatically identify spells being cast while you are under its effects[3].

[1] this is basically "here's how counterspell's detection works, and why you can't hide spell-casting."
[2] because I personally think the school of magic is useless unless you meta-game hard and even then it's pretty bad. This would give you something like "it's a sensor" for alarm or "feels like pent-up explosive energy" for the explosive runes variant of glyph of warding.
[3] instead of using Xanathar's reaction-identify.

Why? Because I like giving out more information. And it seems that in a fantastic world, people would have some sense for active magic. It's thematically quite common--the whole "hairs standing up on your arm in the presence of serious power" or "I can feel his aura/ki" thing.

[olskool]

I'm considering doing the following:

1. (General rule, available to everyone). All creatures can sense the following events within 30 feet of them, as long as there is a clear path to the source. This is a binary sense (yes/no/present/absent) and does not give any targeting information or other information.
1a. A spell of 1st level or higher being cast. Subtle spell counters this.
1b. A major magical effect, such as that of an active Very Rare or rarer magical item or an ongoing, free-standing spell effect of 5th level or higher. Note that spell effects anchored in a person (ie spells active on a person) do not count for this.
1c. Substantial environmental magic, such as being in the vicinity of the lair of a legendary creature.

2. (For all PCs and monsters of CR or level 11+ and anyone capable of casting 3rd level or higher spells). The range extends to 60 feet and you can now detect cantrips and free-standing spells of 3rd level (or Uncommon items). For spells being cast, you know who is casting them if you can see the caster[1]. Otherwise you simply know a spell is being cast.

3. (For all PCs and monsters of CR or level 17+ and anyone capable of casting 6th level or higher spells). You have the passive effect of detect magic (ie getting the "ping") as a passive sense.

4. The warlock invocation removes concentration from detect magic.

5. Detect magic also gives you a sense of the intent of the magic[2] and you automatically identify spells being cast while you are under its effects[3].

[1] this is basically "here's how counterspell's detection works, and why you can't hide spell-casting."
[2] because I personally think the school of magic is useless unless you meta-game hard and even then it's pretty bad. This would give you something like "it's a sensor" for alarm or "feels like pent-up explosive energy" for the explosive runes variant of glyph of warding.
[3] instead of using Xanathar's reaction-identify.

Why? Because I like giving out more information. And it seems that in a fantastic world, people would have some sense for active magic. It's thematically quite common--the whole "hairs standing up on your arm in the presence of serious power" or "I can feel his aura/ki" thing.

Just have them make a Proficiency check like using a skill to do it and it shouldn't be too game-breaking.