When I answer they say hello and then hang up

I keep getting  calls from this "unknown caller." I have a call interceptor device. After one ring, callers not on my white list must say their name and the nature of the call and then press a specified extension number to get through, but they always hang up instead.

Not absolutely sure, but I believe this is one of those "State Trooper" charities that call and pressure you for donations.  The call comes from the Birmingham/Alabaster Alabama area.

Received a call on my home phone on 3/4/17 at 1:31 pm.  Wasn't home at the time  working.