Interference is a simple addon to announce interrupts to the party chat. Currently it has no configuration available, and will handle both incoming and outgoing interrupts, in the following formats:
Interrupted Name's Spell (school)
Name interrupted my Spell (school)
I do have plans to add configuration to this, to allow users to select a channel output, change the message format, and disable certain message conditions. Though I can't make promises that I'll implement options "soon". (Be patient, and for now you're free to modify my code to your liking if you "need" configuration.)
This addon is released under the MIT license found here.