class diagram for bank class on low and high acount balance

I am learning system design and stuck at some point. I have a bank class containing balance and account number. I want to trigger alerts on low balance and give investment options on high balance(keeping in mind if I want to extend it in future). How will I design this functionality. Should I make this a part of bank class or a separate class.

For triggering alerts, I am thinking to apply strategy design pattern. Please help me in making the class diagram/design.