It depends. If the device uses bluetooth, then the proprietary commands could be reversed engineered and an app be put together. Imagine sitting next to someone while changing settings on their pacemaker. You get up and leave, and five minutes later the person dies. The chances of someone putting 2 and 2 together are slim, and even if they remembered you, you're just another guy on his smartphone. If the device uses a proprietary communications protocol on another part of the radio spectrum, then a transciever box would be needed to access the medical device. Such a box can be built, but it would be more noticable and would require someone with specialized knowledge. Then, common methods would be cheaper and easier to use.