You know police are not all technically clueless, I hope. The French have plenty of experience dealing with terrorism, cybercrime, and other modern problems as well as the more historical experience of being conquered and occupied, I don't think it's beyond them to game out scenarios like this and preempt such measures.

As France discovered the hard way in WW2, you can put all sorts of rock-solid security around the front door only to be surprised when your opponent comes in by window.