A fundamental tension exists between safety in the common case and security under adversarial conditions for wireless implantable medical devices. We propose a class of new, fail-open defensive techniques for implantable medical devices that attempt to strike a balance between these two goals. We refer to these defensive techniques as Communication Cloakers. Cloakers are externally worn devices, much like computational Medical Alert bracelets. Cloakers protect the security of an IMD when worn, but allow for open access during emergencies if removed.