A person with a heart ailment has gone into cardiac arrest! Where is the nearest defibrillator? In this case, the victim is wearing it.
The medical technology company ZOLL has developed LifeVest, a wearable defibrillator. It continuously monitors the user's heart activity. When the user goes into cardiac arrest, it squirts electrode gel onto the chest, then sends appropriate electrical shocks into the heart.
The LifeVest is designed for children who weigh at least 41 pounds and have a chest measurement of at least 26 inches. You can read more about it and watch a video at Damn Geeky.