I am interested in adding to my home a system for detecting which room each occupant is in. It would need to be passive, because asking everyone to place their hand on a reader each time they passed through a doorway wouldn’t be practical. Instead, I’m wondering if it might be possible to adapt a portal system like those used as antitheft systems in retail establishments. I understand how those work—a tag is detected if it passes through the portal without being deactivated—and that the system would have to be rather different to work by reading the ID of a tag as I would need for my application. I also understand that RFID tags like the xEM are very short range (<10cm) devices when used with the normal readers designed for them.
But, if it were possible to embed a large coil in a doorframe (alternatively, it could be mounted on the surface of the frame for minimum attenuation—I don’t really care what it looks like as long as it works reliably) and feed it enough power to create a strong field, might it be possible to create a circuit capable of activating an xEM RFID implant and detecting its return signal over a distance of, say, 50cm?
Surely I’m not the first person to have thought of this idea, but days of Googling all the variations I can think of have hasn’t gotten me anywhere. Opinions on whether it might be a practical idea? If so, could someone point me to any resources that might help me get started? I’d like to build the system myself if possible (I’m experienced with electronics), but I’d very much like to have it happen in any case so if necessary I’m willing to throw a fairly large amount of money at it to make it work. Also, I’m currently doing a major remodeling project on my house, so I have complete access to the interiors of the walls and doorframes and could easily install any size coil of antenna wire in a loop all the way around each doorframe if that would be the most effective configuration to work with the coil antennas in the Dangerous Things implants.