• When the shield is absent and an adversary with 100 times the shield’s power transmits unauthorized commands, the IMD responds from distances as large as 27 m.

• When the shield is present the high-powered adversary’s attempts succeed only from distances less than 5 m, and only in line-ofsight locations. The shield always detects high-powered adversarial transmissions and raises an alarm. We conclude that sufficiently high-powered adversaries present an intrinsic limitation to our physical-layer protection mechanism. However, the shield’s presence reduces the adversary’s success range and informs the patient, raising the bar for the adversary’s attempts.

an image