The Slave Collar is an item used by the Slavers found in Paradise Falls. The Slave Collar is a quest item and so cannot be removed from the player's inventory. The Collar is capable of initiating a self-destruct feature, killing the wearer. The signal for the feature is apparently sent out from Paradise Falls.
Occassionally, you may encounter an Escaped Slave who will run up to you and request your help. They want you to remove the Collar before it explodes. To remove it, the player must have Explosives skills. Alternativley, a high Science skill will suffice. Failing to remove the Collar will result in its detonation and the death of the slave.