They were small with strong adhesive on one side. I was able to attach one to the underside of Daisys desk while she was distracted. Rob had installed a relay while we were partying that would collect the data and forward it to my laptop when I called for it.
In appearance it was just like a telephone junction box that was stuck to the exterior brick with strips of strong adhesive.
A conduit that went down into the soil below held the wires that formed the antenna.