Quest Rule - Link's Awakening style compass

[_L_]

The only difference is: when you enter a screen which contains an un-collected Key, Level-Specific Key, Magic Key or Boss Key as its Item or Special Item, the compass plays a four-note sound effect.

[ECNM]

I was going to suggest this myself! In other words, I approve.

[Shoelace]

Or a screen flag, that makes the sound when you enter the room if you have the compass. That way compasses aren't just limited to keys.

[CJC]

Shoelace is right. Screen flags are more versatile and easier to use than a quest rule.

I agree wholeheartedly.