When I answer, they hang up.

Legitimate security company called Vector Security. They mainly cover businesses, large & small. They call when an alarm is going off. If they are calling you then politely tell them they have the wrong number. They obviously will not call back.

I received a call from this person at 11pm last night and 330am this morning. I don't know who they are or what they want but, I need my sleep!

This is a legit security company calling to notify me about alarms going off at a company that I no longer work for.  It seems my lazy ex-boss has not taken me off the call list.  Since I quit it will probably never get done. Everyone there is waiting for someone else to get things done while they sit around pretending to work. ;p

called trying to get security information from me.

I just got a call from them as well