Caller ID is just the number. They leave no message. I do not call them back.
I received the call this morning. I googled the number but saw little. I googled it later in the day and there was a lot more (although most of it was pretty useless). This tells me the number is new and became very active very recently.
One site said 18 of 18 users reported it as spam (although no comments were left). On another site someone said "The callback number used in the message was not the same as the number from which the call was received, 855-639-3615." According to 800notes, a little less than 2 years ago that number was associated with home security systems.
So pretty clearly it's a crap call. Best current theory is someone selling home security systems.
We got a call from this number today at 12:36 pm. The caller ID listed only the number. It wasn't blocked by our call blocker but by our phone service, which has anonymous call rejection. Also, the number is spoofed. When I called back (our number is hidden by default on outgoing calls), I heard a recording which said the number is no longer in service.