Is my homebrew Burning Ears spell the right spell level?

Question

I have designed this spell:

Burning Ears

8th-level divination

Casting Time: 1 minute
Range: Self
Components: S, M (an earwig or a hollowed out animal horn)
Duration: Concentration, up to 1 hour

Classes: Bard, Sorcerer, Warlock, Wizard

For the next hour, you listen very closely for the sound of your name. If any creature on the same plane as you uses your name to refer to you, you are able to eavesdrop on their conversation. For one minute, you can hear what takes place as if your ears are in the room.

If another creature on the same plane as you uses your name to refer to you within the hour, you can choose to turn your attention to that one, or continue listening to the current one.

I currently have it listed as 8th-level. Is this an appropriate level for the spell?

On one hand, there is no save, and no way to detect that it is happening. It has no limit on how far the spell reaches. However on the other hand, it only lets you hear, not see, it can be blocked by Nondetection, and if your enemies find out you use this spell, they can simply stop using your name to refer to you.

Some changes I am considering:

• Duration: Concentration up to 8 hours instead of 1 hour
• Duration of eavesdropping of 5 minutes instead of 1 minute
• Text that specifies that you feel a momentary sharp pain in your ears when you key in. Maybe it could even deal 1 psychic damage?
• A Wisdom check by the targets that reveals a general feeling that they are being watched if they succeed

Answer 1

Player characters wouldn't use this

Very few player characters are so famous that people would refer to them by name. Even if an NPC was specifically making plans to kill them, the NPC would probably be talking about the group as a whole ("the adventurers", "the heroes", "those jerks") and wouldn't refer to them by name.

It's also sort of a weird mechanic if a player character tells you "okay, I'm casting this spell now, tell me if anyone in the world says my name in the next hour". I don't think it would be fun for the DM to deal with a request like that.

A major NPC (we're all thinking of Voldemort) might use a spell like this, if they were very famous and were interested in learning about people's plots against them. But it seems too weak for eighth level.

It seems too weak for eighth level

In terms of actual balance, this is a divination spell, so we should compare it against other divination spells such as scry and commune. Either scry or commune is better if there's a specific person that you think might be plotting against you. (Especially commune -- you can just go talk to your god and ask "hey, can I trust that guy?" and get a yes-or-no answer.)

If there's not a specific person you think might be plotting against you, this spell is sort of viable, but still not very good. The spell doesn't even reveal who's doing the plotting, unless they happen to refer to each other by name during the minute you're eavesdropping. You just get a message saying "hey, that Voldemort guy is pretty dumb." and then "yeah, I don't like him either!", and hearing random people insult you anonymously isn't something there's a lot of demand for.

If I wanted to make this a useful spell for eighth level, I'd add the ability to know who spoke the caster's name and where they are currently. Then I'd make it a twenty-four hour spell with no concentration, because there's not much value in doing this if you can't keep it up constantly. I definitely would not add any tip-offs alerting people that they had been noticed.

But what I'd actually do is I'd replace the spell with a magic item, like a headband that the villain wears that gives him this power when attuned. Most people aren't going to want this, so there's not really a need to make it a learnable spell.