"Have there been any reports of people targeting magic users? I doubt this was an isolated incident."
Cyrielle considers her options. Those bracelet units were undoubtedly useful, however, they lack sufficient security judging by how Grandiose most likely intercepted signals and used the signal locations to track them. Currently, it seems likely that those bracelets broadcast the thoughts and only ones with the same frequency can receive them. However, interception would be a mere matter of finding that frequency. The most simple solution that immediately comes to mind would be to encrypt the information and split it, sending it across different frequencies through different bracelet paths, of course that only reduces the risk of interception.
A more secure though difficult option would be to send it through a secure network. Of course, establishing one is rather difficult so a pre-existing one could be used to make it feasible. Two options are salient here: Void and Fate.
Void is significantly easier to establish as there is evident knowledge of using it for magic, case in point, Abraxas. However, that same ease from knowledge means that it does not so much as prevent interception as much as it limits the potential interceptors to people who have a degree of void control.
Fate is the harder of the two options as it contracts based on a set of criteria which at present, Cyrielle was the only one known to fulfill, however, Annie and Wheatley also are capable of using it so that increases the knowledge base. Though it would be far more secure as Annie and Wheatley are aspects of Fate, hence, they would be capable of stopping any eavesdropping attempts.
Of course mind transfer would still have to be on an unsecure channel, seeing as while encoding messages and sensory data as Void or Fate signals shouldn't be too difficult, it probably isn't possible to encode an entire mind nor would encrypting be much of a feasibility.
Still, the bracelets also need system to prevent signal interception from it directly before encryption and/or encoding.