It stands to reason that it should be fairly difficult to detect & intercept over-the-air signals. Although, even with Reva's wireless hack ability, she would still need to get within 20 feet of them. I don't think it's a good idea to risk getting too close, because beside the usual possibility of being detected visually, if the hack fails (Reva needs to roll 15 or higher) it could trigger a countermeasure & spook them.