Joy Detectors were built by Dr. Faraday as a way to detect any Downers roaming about in Hamlyn Village, during the events of They Came From Below DLC, Faraday uses some of the robotic parts of her robot servants to invent bigger and better Joy Detectors.
After the events of the DLC and before the events of the main game, Faraday goes against the Exectuive Committee and refuses to create any more of her inventions and therefore gets locked away in her own home.
The player will come across various kinds of Joy Detectors as they traverse Hamlyn Village and the Parade District. There are a couple ways to bypass these detectors.
Downer Detectors are devices with a glowing yellow beam that turn red if the player walks through it without any Joy in their system, an alarm will go off and a nearby Spanker will charge up to electrify the player, any nearby Wellies will also aggro onto the player.
In order to deactivate these, the player will have to find a nearby control box, follow the yellow cable connecting the two.
If the player gets close to the headmistress without any Joy in their system, they will give them three seconds to move away from the area before summoning an electric circle around the player in an attempt to stun them while Wellies aggro onto them. They can only be deactivated in the Parade District via control boxes.
Peepers are drones that doesn't exactly scan the player's Joy amount, but rather if they are doing anything wrong. They only come out during night time apart from a select few that guards particular parks or houses.
Peepers are higher off the ground and can therefor get a better view of the player, when spotted they will charge up their in built spanker and electrify the player. They can be damaged by any throwable weapon such as Darts, Glass Bottles or even Bangers.
Spankers come in three forms, the TVs, the pillars and a knob that hangs off the ceilings and walls of buildings. The TV spankers on the streets cannot be deactivated, but the TVs that are connected to a nearby control box can.
Spankers cannot be triggered on their own, they usually need some other device to charge them up, so if the device that activates the spanker is down, the spanker won't get to the player.