If you do not recognize the number, don't pick up! If you do not have caller ID, get it.
These scammers never leave messages, which is how you know they are scams.
Any legitimate caller is going to leave you a message.
Please, I get several calls from the same car warranty scammers on many different numbers. They always start with "My name is Heather" . . . and then offer a way to opt out. Then calls again the next day from a different number.