We have an ancient and antiquated bell system that doesn't work in large swathes of the campus. To supplement it, in areas the bells do not work, your Cisco phones act as bells.
You can't miss the actual bell. It's quite loud. If you get the bell over your Cisco phone, the Cisco bell sound is piercing, and hard to miss as well. If you are regularly letting your students out of class because they claim the bell rang, stop. Unless you're legally deaf, you aren't going to miss the bell, so believing your students who are just trying to get out of class early is not the answer. Check your clock on your phone or laptop, as those are synced to the time. Our bells ring ~20 seconds ahead of the correct time. If your laptop or phone gets a minute or longer ahead of the time the bell is supposed to ring, then you need to let the tech coordinator know so your phone can be set up to the bell schedule.