Remote doors can only be activated by a Door Servo, connected to any servo-activating mechanism such as Pressure Pad, Door Control System, etc. The Door Servo motor part has to be on top of the door for it to work.
The difference from the rest of the doors is that nobody can open it, only by remote control. Or by manually setting Locked Open/Shut as usual. Keep in mind that a Door Servo can be installed on any door, they are not restricted to Remote Doors.This means that even when a Prisoner steals the keys from some guard (by beating them unconscious or killing them), he won't be able to pass through this door. However, as usual, he will try to kick the door down.
Remote doors serve virtually no purpose as cell doors. Normal cell doors already function automatically by remote control (regime schedule) and stay open during all times except for Sleep or Lockdown. Remote doors are intended to give you remote control for other areas of the prison and can be used to separate cell blocks leading to the cells, or for extra security where desired. But since cell doors are already automated, they are sitting open most of the time anyway when placed in a normal cell.
It is more efficient to install the servo for the door and have it attach to a door control prior to installing the door. If your workers install the door beforehand, they may become stuck waiting for the door to open. To fix this issue, manually lock the door open until installation of the servo is done and the door control connection has been established.You can achieve a 'chain-effect' in door functionality when wiring several servos up one after the other. Start off at one servo and link it to another and yet another. The result is, that when the first door opens, the other will follow subsequently. This way, you can have several doors open up when a person starts passing the first one. It works in both directions, just watch the pulsating arrow on the wire to know which door follows.