This sounds virtually unenforceable. Gated and protected phones and computers are the domain of highly secretive projects, and cost an arm and leg to enforce. It means searching personnel as they enter the protected zone for watches, phones, computers, tablets, etc. Since phones geolocate and Google has this data, the protected zone needs to be enormous. Like, an entire city block to prevent the algorithm from detecting the handover. If you somehow overcome this, you need to ensure that the employee never ever, for any reason ever logs into anything personal on the gated devices. It basically means preventing them from using the internet. How productive are developers who can't go online? It also means zero cross-communication to outside the zone. No emails to/from home/work. No sending files, no checking emails, no taking calls (someone could easily use a connected service to make the call). This "air" gap is extremely difficult to enforce.

I've ever seen anyone successfully pull off this kind of secrecy in anything larger than a 10 person team, and the cost was insane.