A client has a large warehouse (15k+ sq.ft.) and has had problems leaving the door open late at night and things "walk" away.
He wants to locate a "buzzer" outside that will go to some sort of horn inside that will get get the crew's attention that someone is at the door.
Any suggestions on manufactures for this product? I'm not even sure exactly what I'm asking for even though I've seen them a hundred times.
I do want to make sure this is industrial/commercial grade since the buzzer may endure some abuse.