This little weapon operates just like a standard +1 dagger until it comes within sighting distance of any evil-intentioned monster.  Then it will begin calling out, in a very loud, high-pitched voice, to these nearby evil creatures in their native tongue, and will curse and insult them intolerably.  If the encountered creature does not speak any language, the dagger will emit a screaming wail sounding remarkably like a poor, defenseless animal waiting to be eaten.  This dagger can easily "teleport" into a character's possessions, like any cursed weapon, if the owner makes a simple attempt to discard it.

Source:  Dragon Magazine #77, 1983, page 21

Proficiency with a dagger allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Finesse, Light, Thrown