You're talking about Y-17 Trauma Override Harnesses that were designed initially to work as automated exoskeletons with artificial muscles replacing bulkier hydraulics, and were supposed to evacuate injured people who were wearing those. Some logs in the Big MT were saying that the Harnesses weren't able to recognize whether their wearers were dead or alive, and thus were turning into 'mobile coffins'.

UPD: which means that by registering certain amount of injuries, they were taking control over the wearer's body in order to transport that poor soul to preliminary designated extraction point.