I had a neighbor who had one of those. Every time it defibrillates you is like getting kicked in the chest by a mule. He finally had it turned off.
And when it springs into action, anyone in contact with the wearer can be given a jolt as well. DH would abruptly push me aside when he felt it might suddenly bolt. Fortunately, after some time, finding the wires had corroded, and his heart had become much stronger, they were able to remove the devise with no adverse side effects. That was ...8 or 10 years ago IIRC