The concept of a bell ringer is to get the class started as soon as possible. The idea is not to watch value time getting a class starter. Consider your class - how much time is lost at the start of every day and after the break? Add up that time by week, month and semester, and you will find that days can be lost because of how you start your class.
Some ideas for bell ringers
Write a question on the board and require students to answer it upon arrival. The question can involve reviewing from the day before, introduction into that day's lesson, requiring students to apply what they learned for far, etc.
As part of their sign-in process students need to answer a random question to get entry into the classroom. Wrong answer and they need to wait.
Use technology - put a diagram, chart, etc. on the projector and have them analyze it.