Burglar alarm scam or worse. NEVER answer this line. I did and hung up after listening. It seems they have discovered a live line and keep calling using a different number. These days, if you do not recognize a phone number and the caller refuses to leave a message, you do not need them. If you have little old lady relatives, like I do who seem unable to leave a simple message on a machine, even if the message says "call me" , it's time to update their telephone etiquette. Or provide them with a pager.