I have several of the lacrosse technologies units. Check Amazon for models and prices. The concrete and steel could be blocking the signal for sure. I have the remote unit in my cellar and the main unit in the house about 30ft away and they work great together but then they are only going through air and wood, not steel and concrete. Worst comes to worse use a wired one and mount it on the door and send the wire through the vent opening.
Happy to hear your making some progress!
Happy to hear your making some progress!