The collar constantly emits a red light that will strobe on and off. It is very similar in design to the slave collar from Fallout 3. The collar is used to control slaves and can deliver a painful, potentially deadly, electric shock when activated. The collar itself provides no Damage Resistance and no other bonuses.
Pickpocketed from traders in the Nuka-Town market and elsewhere in Nuka-Town (requires Pickpocket rank 4), or looted from their corpses.
If Open Season is completed and the traders freed, they will still have their shock collars on.
The pack captives in the amphitheater constantly respawn unless The Pack is attacked or rebels in Power Play, making them a good source for shock collars.
While not actually appearing in the base game of Fallout 4, Cait mentions her parents using a shock collar on her to sell her into slavery.
↑Cait: "Then me eighteenth birthday arrived, and I found out why they kept me around.They slapped a shock collar around me neck and sold me to slavers. They didn't even care enough about me to say goodbye." (Cait's dialogue)