Tartarus is a mod designed to solve certain unavoidable problems in Minecraft prisons.

Card Reader:

Emits a redstone signal when activated with a valid keycard. Can hold up to 9 keycards, the first of which being the admin slot. Only a keycard matching the one in the admin slot will enable admin mode when unlocked, allowing the user to change the keycards inside.

Redstone Keycard:

Can be inscribed with an inked quill using the /write command. Used to unlock Card Readers. Can be enchanted with curse of vanishing.

Inked quill:

Used to inscribe access codes on Redstone Keycards. To inscribe a keycard, hold the quill in your offhand and the keycard in your main hand and type /write <access code>.

Polished Speaker:

Can type messages in chat to players up to 32 blocks away when activated by redstone, making a gonging sound in the process. Type a message in the textbox and press save to set it, or place a dye in the dye slot to change the color of the message. Rename the speaker in an anvil to change the prefix.

Echo Feeder:

Automatically feeds players within 16 blocks using food from it's inventory when powered by a redstone signal. Can feed multiple players at once, but will not feed players food that they don't have room for. Will apply special effects for some food (rotten flesh, raw chicken, spider eyes, etc.).

Control Collar:

Allows targeting by players with a control rod matching the inscription on a collar worn by another player. Can be enchanted with helmet enchantments, including curse of binding. Can be inscribed the same way a Redstone Keycard can.

Control Rod:

Allows greater control over players with a matching Control Collar using the /asset command. Can also be enchanted with sword enchants.

/asset target <player> will set a player as the current target. If said player is wearing a matching collar, shift right clicking on blocks will simulate right click by the collared player, as if they had interacted with them themselves. This can be used to force players to set their spawn at a bed/respawn anchor. The player holding the control rod can also right click the air to send a harmless but painful jolt to the targeted player.
/asset diagnose <player> will display a collared players name, health, food, location, and the durability of their collar.
/asset leash <player> <range> will create an electronic leash binding a collared player to the player who ran the command. If the collared player leaves the radius of the leash (at most 32 blocks), they will be paralyzed and their collars will sound an alarm.
/asset unleash <player> will deactivate an electronic leash on the specified player.
/asset terminate <player> will activate a killswitch in a players collar, giving them wither III for 30 seconds.

Ender Jammer:

When powered by an eye of ender, Ender Jammers block ender pearl teleportation in a 32x32x32 cube around them. Any players that would have been teleported either in or out of this area now just take fall damage instead. When broken, powered Ender Jammers don't drop their eye of ender, unless broken by silk touch.

Tartarus.